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I 

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22  19 
FEB    5' 


1984 


1762S-S 


FIELD  COLUMBIAN  MUSEUM 

PUBLICATION  5. 
ZOOLOGICAL  SERIES.  VOL.   i,    No.    i. 


ON  THE  STRUCTURE  AND 
DEVELOPMENT 


OF    THE 


VERTEBRAL  COLUMN  OF  AMIA 

WV. 


BY 


O.   P.   HAY,    PH.   D., 

Assistant  Curator  of  Ichthyology. 

D.  G.   ELLIOT,  F.  R.  S.  E.,  Curator  of  Department. 


CHICAGO,    U.   S.  A. 
October,   1895. 


VII' 


CONTENTS. 


1.  Description  of  the  gross  structure  of  the  vertebral  column. ...    5 

2.  The  minute  structure  of  the  vertebral  column 15 

3.  Discussion  of  the  vertebral  column  of  fossil  fishes 20 

4.  Discussion  of  the  vertebral  column  of  the  higher  vertebrata. .  .24 

5.  The  origin  and  development  of  the  vertebrae  of  Amia  dur- 

ing its  earlier  stages 25 

6.  Further  consideration  of  the  vertebral  column  of  fossil  fishes.. 39 

7.  Further  discussion  of  the  vertebral  structure  of  Teleostei 42 

8.  Further  consideration  of  the  vertebral  column  of  living  and 

extinct  Amphibia 45 


ON  THE  STRUCTURE  AND  DEVELOPMENT  OF  THE  VERTE- 
BRAL COLUMN  OF  AMIA.— O.  P.  HAY,  PH.  D. 


I.       DESCRIPTION    OF    THE    GROSS    STRUCTURE    OF    THE    VERTEBRAL 

COLUMN. 

For  our  knowledge  of  the  vertebral  column  of  the  fish  Amia  we 
are  indebted  to  a  considerable  number  of  writers,  whose  works  will 
be  found  in  the  list  at  the  end  of  this  paper.  Their  views,  so  far  as 
they  concern  our  present  purpose,  will  receive  consideration  as  our 
discussion  proceeds. 

In  again  calling  attention  to  the  spinal  column  of  this  fish,  we 
must  first  of  all  consider  a  peculiarity  which  has  struck  all  investiga- 
tors, and  which  distinguishes  this  species  from  all  other  living  osse- 
ous fishes.  This  peculiarity  consists  in  the  possession,  throughout  the 
greater  portion  of  the  tail  region,  of  apparently  twice  as  many  verte- 
bral bodies  as  there  are  myomeres  and  neural  and  haemal  arches. 
Franque  (26)  appears  to  have  been  the  first  to  remark  on  this  struc- 
tural feature  of  this  fish.  He  regarded  those  vertebral  centra  which 
are  devoid  of  upper  and  lower  arches  as  intercalated  vertebrae 
similar  to  those  which  are  found  in  certain  sharks  and  rays.  He  says: 
'•  Sunt  igitur  corpora  vertebrarum  inter  vertebras  intercalata." 
He  refers  to  the  fact  that  among  the  Rays  Rhinobatus  has  intercalated 
vertebrae,  while  among  the  Squali  Sphyrna  malleus  has  intercalated 
superior  arches.  Almost  all  other  writers  who  have  dealt  with  the 
subject  have  adopted  the  same  interpretation,  while  it  is  the  express 
purpose  of  a  recent  paper  by  Ludwig  Schmidt  (56)  to  establish  this 
view.  On  the  other  hand,  Dr.  G.  Baur  (9)  and  Dr.  Carl  Zittel  (60) 
hold  that  the  two  segments  of  the  vertebral  column  which  are  found 
in  each  of  the  myomeres  in  question  are  "centra"  and  "  intercen- 
tra,"  (pleurocentra*  and  hypocentra.),  corresponding  to  those  ele- 
ments which  together  make  up  a  vertebral  body  in  some  of  the  Stego- 
cephali. 

I  signify  my  acceptance  of  the  opinion  that  the  whole  vertebral 
column  of  the  ancestors  of  Amia  was  composed,  in  each  myomere,  of 

*The  term  centrum  has  long  been  in,  use  to  distinguish  the  principal  portion  of  the  vertebra 
independently  ot  any  theory  concerning  its  origin  and  composition.  To  apply  now  this  term  to  dis. 
tinguishone  of  the  elements  that  may  enter  into  the  construction  of  a  vertebral  body  would  intro- 
duce confusion.  I  prefer  therefore  to  employ  in  this  paper  pleurocentrum  and  fiypocentrum  to  des- 
ignate the  elements  of  the  body. 

5 


'•t 


6  FIELD  COLUMBIAN  MUSEUM — ZOOLOGY,  VOL.   i. 

the  two  elements  named,  and  that  in  the  caudal  region  of  this  fish 
we  have  both  of  these  elements  present,  and  still  distinct  from  each 
other.  I  find  it  impossible  to  ignore  the  results  of  palaeontological 
researches  when  they  are  exhibited  in  so  clear  a  light.  These  results, 
which  reveal  an  extraordinary  similarity  between  the  stegocephalous- 
vertebral  column  and  that  of  so  many  of  the  earlier  osseous  fishes, 
cannot  be  set  aside  lightly,  merely  because  there  is  in  the  tail  of  cer- 
tain Elasmobranchs  an  evident  duplication ;  at  -least  not  until  it  has 
been  shown  by  embryology  that  the  vertebral  bodies  in  the  two  cases 
arise  in  the  same  way ;  and  this  has  certainly  not  yet  been  done. 

If  we  shall  regard  a  pleurocentrum  and  a  hypocentrum  in  the  tail 
as  together  constituting  a  vertebral  body,  the  total  number  of  these 
in  the  whole  vertebral  column  will,  of  course,  be  considerably  reduced 
below  the  number  usually  given  by  authors.  Franque  says  that  the 
number,  including  the  intercalated  ones,  is  commonly  ninety-two, 
although  the  number  may  vary  somewhat.  Of  this  number  thirty- 
seven  or  thirty -eight  belong  to  the  trunk.  L.  Schmidt  found  in  one 
skeleton  thirty-nine  vertebrae  in  the  trunk  and  forty-seven  in  the 
tail.  In  his  figure  of  another  specimen  he  represents  fifty  segments  in 
the  tail,  of  which  about  fourteen  are  the  so-called  intercalated  pieces. 
The  anterior  four  to  six  caudal  vertebrae  are  simple,  and  resemble  in 
all  respects  those  of  the  hinder  dorsal  region,  except  that  the  lower 
arches  are  closed  below  to  form  the  haemal  canal.  Near  the  end  of 
the  tail,  again,  the  intercalated  pieces  are  not  developed.  Therefore, 
counting  pleurocentrum  and  hypocentrum  as  one,  we  find  about  sev- 
enty-five vertebra?  in  the  whole  column,  although  the  number  may  be 
from  one  to  three  less. 

Externally  the  vertebrae  of  Amia  differ  from  those  of  most  other 
osseous  fishes  in  the  almost  total  lack  of  excavations,  bony  ridges  and 
subsidiary  processes.  Those  of  the  trunk  especially  may  be  regarded 
as  approximately  circular  disks,  each  with  a  conical  excavation  at  each 
end.  These  disks  become  gradually  shorter  as  we  move  from  the 
hinder  dorsal  vertebrae  towards  the  head.  In  the  tail  the  two  ele- 
ments, pleurocentrum  and  hypocentrum,  taken  separately,  are  con- 
siderably shorter  than  a  hinder  dorsal  vertebra ;  but,  if  we  consider 
the  two  elements  as  constituting  a  single  vertebral  body,  we  find  that 
their  combined  lengths  usually  exceed  somewhat  that  of  a  dorsal  cen- 
trum, while  the  length  of  an  anterior  caudal  vertebra  is  only  about 
seventy-seven  per  cent  of  that  of  a  hinder  dorsal  vertebra.  As  far  for- 
ward as  the  twenty-third  dorsal  vertebra  from  the  head  the  length  of 
each  vertebral  body  remains  nearly  the  same  as  that  of  the  hinder- 
most.  In  front  of  this  they  generally  grow  shorter,  so  that  the  most 


OCT.  1695.  VERTEBRAL  COLUMN  OF  AMIA — HAY  7 

anterior  is  but  little  more  than  half  the  length  of  the  twenty-third. 
Schmidt's  description,  but  not  his  figure,  would  lead  one  to  suppose 
that  the  first  two  vertebrae  behind  the  head  are  shorter,  when  com- 
pared with  the  succeeding  ones,  than  they  really  are. 

In  transverse  section  the  dorsal  vertebrae  are  somewhat  broader 
than  high,  the  perpendicular  axis  of  the  first  dorsal  being  about 
eighty-five  per  cent  of  the  transverse  axis.  As  we  move  backward, 
the  form  changes  somewhat,  so  that  sections  become  more  and  more 
nearly  circular,  the  hindermost  dorsal  body  being  nearly  perfectly  so. 
The  caudal  centra,  on  the  other  hand,  become  more  and  more  com- 
pressed towards  the  tip  of  the  tail.  Thoroughly  macerated  verte- 
brae, as  well  as  sections  through  decalcified  vertebrae  in  various 
regions,  show  that  the  notochord  has  not  suffered  complete  constric- 
tion, but  runs  continuously  through  the  vertebral  column. 

It  is  no  unusual  thing  to  find  the  pleurocentrum  and  hypocen- 
trum  of  some  of  the  myomeres  of  the  middle  portion  of  the  tail  con- 
solidated. Stannius  (58,  p.  21)  had  observed  this  union  of  elements, 
and  that  it  occurred  at  different  points  in  different  individuals. 
Schmidt  has  called  attention  to  the  same  phenomenon,  and  has 
figured  such  a  resulting  vertebra.  In  such  cases  there  is  the  closest 
possible  resemblance  between  the  vertebra  so  resulting  and  one  of 
the  anterior  caudal  vertebrae.  At  the  same  time  there  can  be  no 
doubt  concerning  the  complete  homology  of  an  anterior  caudal  verte- 
bra and  any  of  those  of  the  dorsal  region. 

On  the  other  hand  there  may  occur  a  union  of  the  elements  of 
different  vertebrae.  A  specimen  in  my  possession  shows  an  evident 
case  of  the  consolidation  of  the  hypocentrum  with  both  the  pleuro- 
centrum in  front  of  it  and  the  one  behind  it. 

Even  if  we  should  not  be  able  to  find  in  the  middle  tail  region  a 
vertebra  formed  by  such  apparently  abnormal  union  of  pleurocen- 
trum and  hypocentrum,  we  might  find  it  instructive  to  compare  these 
elements  of  any  myomere  with  a  posterior  dorsal  and  an  anterior 
caudal  vertebra.  The  general  form  of  the  two  elements  taken  to- 
gether is  the  same  as  that  of  the  simple  vertebral  body.  In  the  case 
of  the  middle  tail  segments,  the  upper  and  lower  arches  rest 
on  the  hinder  element,  the  intercentrum.  In  the  dorsal  region  the 
arches  repose  on  the  hinder  half  of  the  vertebral  body.  In 
"both  the  middle  and  the  anterior  tail-regions  the  upper  and  the  lower 
arches  are  separated  by  suture  from  the  corresponding  bodies.  If 
we  should  form  our  conclusions  regarding  the  composition  of  the  dor. 
sal  and  the  anterior  vertebrae  from  what  a  macroscopic  view  of 
the  parts  affords,  we  would,  I  think,  conclude  that  they  have  been 


8  FIELD  COLUMBIAN  MUSEUM — ZOOLOGY,  VOL.   i. 

formed  through  a  union  of  distinct  parts,  whether  these  be  regarded 
as  pleurocentra  and  hypocentra  or  as  principal  and  intercalated  ver- 
tebrae. 

With  reference  to  the  relations  of  the  upper  arches  to  the  verte- 
bral bodies,  authors  have  not  been  wholly  accurate.  Franque  figures 
three  vertebral  bodies  and  two  superior  arches ;  the  bases  of  the  lat- 
ter reposing  equally  on  the  upper  surfaces  of  two  contiguous  ver- 
tebral bodies,  so  that  the  upper  arches  are  intervertebral  in  posi- 
tion. In  his  figure  of  the  complete  skeleton,  he  represents  the  bases 
of  all  the  upper  arches  of  the  dorsal  region  as  resting  in  a  similar 
way  intervertebrally.  The  bases  of  the  succeeding  simple  vertebrae 
are  represented  as  resting  almost  wholly  on  the  bodies  of  their 
respective  vertebrae,  while  the  upper  arches  of  the  remainder  of  the 
tail  are  borne  by  their  respective  intercentra.  The  following  quota- 
tion from  Franque  is  produced: 

' '  Inter  apophysin  superiorem  et  corpus  utrimque  in  parva  f os- 
sula  pauxillum  cartilaginis  inclusum  est,  quod  in  spuriis  vertebris  rep- 
eris,  cui  cartilaginis  apophysis  affixa  est,  et  eo  quidem  modo  ut  usque 
ad  locum  quendam  unaquaeque  apophysium  duobus  vertebrarum  cor- 
poribus  addicenda  sit." 

Shufeldt  (57)  reproduces  Franque's  figures,  and  states  that  the 
bases  of  the  neural  arches  "  articulate  between  each  consecutive  pair 
of  vertebrae,  these  latter  having  a  form  to  accommodate  themselves 
to  this  unique  condition."  Furthermore,  in  Franque's  figures  the 
hinder  border  of  the  base  of  each  arch  is  represented  as  coming  into 
contact  with  the  anterior  border  of  the  next  base  behind. 

Schmidt  refers  to  Franque's  and  Shufeldt's  descriptions  and  fig- 
ures. He  affirms  that  he  has  not  been  able  to  find,  in  his  specimens, 
the  upper  arches  either  to  be  placed  between  the  vertebral  bodies,  or 
to  come  into  contact  by  their  adjacent  basal  borders.  In  both  his 
text  and  his  figures  he  represents  the  upper  arches  of  the  whole  dor- 
sal region  as  sitting  on  the  hinder  half  of  their  respective  bodies,  and 
extending  over  the  next  body  behind  by  only  a  little  process;  also, 
as  having  between  the  successive  bases,  even  in  the  region  close  to 
the  head,  a  considerable  interspace.  In  so  doing  he  has  fallen  into 
as  great  an  error  as  that  of  the  authors  whom  he  attempts  to  correct, 
but  of  an  opposite  kind. 

When  we  come  to  examine  these  parts  accurately,  we  find  that 
in  the  hinder  portion  of  the  tail,  where  pleurocentrum  and  hypocen- 
trum  are  both  developed,  the  neural  arches  have  their  bases  ex- 
panded anterio-posteriorly,  and  rest  almost  wholly  on  the  hypo- 
centra.  Nevertheless,  the  anterior  process  of  the  base  projects 


OCT.  1895.  VERTEBRAL  COLUMN  OF  AMIA — HAY  9 

forward  somewhat  over  the  hinder  border  of  the  pleurocentrum  in 
front,  while  the  hinder  border  of  its  own  hypocentrum  is  left 
somewhat  uncovered.  As  we  move  forward  we  find  the  neural  bases 
shifted  gradually  backward,  so  that  in  the  case  of  the  most  anterior 
free  intercentrum  the  upper  arch  reposes  on  its  upper  surface,  extend- 
ing neither  on  the  pleurocentrum  in  front  nor  on  that  behind.  In 
the  hinder  dorsal  region  we  find  that  the  neural  bases  are  set  still  fur- 
ther backward,  so  that  their  hinder  angles  begin  each  to  overlap 
slightly  the  anterior  border  of  the  vertebra  next  behind.  This 
backward  displacement  of  the  upper  arches  goes  on  until,  in  the 
anterior  end  of  the  vertebral  column,  the  bases  are  placed  be- 
tween two  vertebrae  and  rest  equally  on  both.  That  is,  if  we 
regard  each  dorsal  vertebra  as  consisting  of  a  pleurocentrum  and  a 
hypocentrum  united,  we  may  observe  that  on  passing  from  the  tail 
to  the  head  the  pairs  of  neural  bases  change  from  a  position  of  rest- 
ing each  on  its  own  hypocentrum  and  partly  on  its  pleurocentrum  to 
that  of  resting  partly  on-  its  own  hypocentrum  and  partly  on  the 
pleurocentrum  of  the  verteibra  next  behind. 

As  regards  the  distance  of  the  bases  of  the  successive  arches 
from  each  other,  we  find  that  just  behind  the  head  they  approach  very 
closely,  if  they  do  not  come  into  actual  contact.  Soon  there 
is  a  space  developed  between  them,  and  this  increases  to  near  the 
end  of  the  tail.  As  regards  the  relations  of  the  arches  to  the  verte- 
brae and  to  neighboring  arches,  it  would  almost  seem  as  if  Franque 
had  drawn  his  conclusions  wholly  from  an  examination  of  the  ante- 
rior end  of  the  vertebral  column,  and  Schmidt  from  the  other  ex- 
tremity. 

At  the  hinder  end  of  the  head  are  two  vertebrae  which  are 
strongly  united  to  the  skull.  Their  presence  is  indicated  by  lines 
running  across  this  portion  of  the  base  of  the  skull,  and  by  their 
movable  neural  arches.  The  halves  of  each  arch  meet  above  the 
myelon,  but  do  not  unite,  nor  are  they  prolonged  upward.  To  the 
upper  ends  of  each  of  these  arches,  or  at  least  the  hindermost  pair, 
is  articulated  a  compressed  inter-spinous  bone  (axonost).  Sagemehl 
has  already  recorded  the  occurrence  of  these  vertebral  bodies,  the 
arches  and  the  axonosts.  The  lateral  halves  of  the  first  arch  behind 
the  head  are  prolonged  above  the  neural  canal  but  a  short  distance. 
To  their  upper  ends  is  articulated  by  a  freely  movable  joint  a  knife- 
shaped  bone,  which  must  be  regarded  as  homologous  with  the  axo- 
nosts which  support  the  rays  of  the  dorsal  fin.  The  succeeding 
arches  increase  gradually  in  length.  To  the  second  is  articulated  an 
axonost  similar  to,  but  longer  than,  the  first  one.  In  two  specimens 


io  FIELD  COLUMBIAN  'MusEU>M— ZOOLOGY,  VOL.   i. 

examined,  the  third  arch  has  no  corresponding  axonost.  The  fourth 
arch  in  one  specimen  has  one  lateral  half  articulated  to  the  next  axo- 
nost, while  the  other  half  lies  free  behind  the  axonost.  The  fourth 
axonost  is  loosely  attached  to  the  upper  extremity  of  the  fifth  arch. 
I  find  only  four  of  these  axonosts,  but  Franque  figures  seven,  only  one 
of  which  appears  to  be  closely  connected  with  a  neural  arch.  Others 
lie  between  successive  arches,  as  do  two  of  them  in  one  of  my  speci- 
mens. Schmidt  very  incorrectly  figures  all  the  anterior  neural 
arches  as  being  extended  oiit  into  lateral  halves  longer  than  those 
which  succeed  them. 

Between  the  lateral  halves  of  each  of  the  neural  arches  and 
overlying  the  neural  canal  is  found  a  pair  of  intercalated  cartilages 
(Fig.  i,  i.  c.).  These  are  vertebral  in  position,  as  is  usually  the 
case  with  the  bony  fishes.  In  Lepisostcus  Balfour  found  similar 
masses  of  cartilages  to  be  intervertebrally  placed.  Above  these  car- 
tilages runs  the  superior  longitudinal  ligament.  In  the  adults  these 
cartilages  become  more  or  less  ossified,  and  the  bony  layer  which 
inve'sts  each  cartilage  is  continuous  with  that  of  the  corresponding 
half  of  the  neural  arch. 

As  regards  the  lower  arches,  we  find  that  those  of  the  middle  of 
the  tail  are  supported  by  the  hypocentra  alone,  and  the  bases  of  these 
arches  lack  a  little   of  reaching  the  anterior  border  of  the  hypo- 
centrum.      In    the    posterior    portion    of    the    dorsal     region    the 
transverse  processes  arise  from  the  very  hinder  border  of  the  verte- 
bral bodies  (Fig.  2).     As  we   advance  towards  the  head  these  trans- 
verse processes  are  moved  a  little  forward,  until  at  about  the  middle 
of  the  dorsal  region  they  occupy  a  position  near  the  middle  of  the 
length   of     the    vertebral    body    (Fig.    3).      Near   the  head    again 
the  processes  appear  again  to  be  slightly  nearer  the  hinder  border  of 
the    body.       With    respect  to  the    level    of     origin    of     the     pro- 
cesses, it  may  be  observed  that  at  the  anterior  end  of  the  vertebral 
column  they  spring  from  the  sides  of  the  vertebrae  halfway  up.    Fur- 
ther back  the  processes  slowly  descend,  so  that  those  of  the  last  dor- 
sal vertebra  arise   from  its  lower  side.     In  length  these  processes 
increase  from  the  first  to  the  middle  of  the  trunk,  and  then  gradually 
grow  shorter  to  the  last  dorsal  vertebral  body.     In  the  tail  the  lower 
arches  are  joined  to  the  centra  by  suture.     Below  the  haemal  canal 
the  lateral  halves  unite  to  form  a  spine.     The  spines  of  the  first  four 
to  six  caudal   vertebrae    are  articulated   to  their  respective  arches 
just  below  the  point  where   the  lateral  halves  have  united.      The 
elevated  origin  of  the  transverse  processes  in  the  dorsal  region  is  no 
doubt  connected  with  the  enlargement  which  that  portion  of  the  body 
cavity  has  suffered. 


OCT.  1895.  VERTEBRAL  COLUMN  OF  AMIA — HAY  n 

Franque  states  that  the  first  vertebra,  omitting  the  two  which 
are  consolidated  with  the  skull,  has  no  transverse  processes,  while 
the  next  has  these,  and  likewise  sometimes  bears  ribs.  In  a  specimen 
before  me  the  processes  of  the  first  vertebra  are  certainly  not  con- 
spicuous, but  they  can  hardly  be  said  to  be  absent.  They  stand  out 
each  as  a  bony  ring  surrounding  a  shallow  pit,  formed  by  a  shrinking 
of  cartilage.  In  this  specimen,  too,  these  processes  support  a  pair 
of  ribs,  each  of  which  is  as  long  as  the  first  five  vertebrae  taken  to- 
gether. Shufeldt  could  find  no  ribs  on  the  first  vertebra.  In 
another  specimen  I  find  no  ribs  on  the  first  vertebra,  but  there  is  a 
pair  on  the  second.  Schmidt  figures  the  first  pair  of  ribs  on  the 
third  vertebra.  In  like  manner  my  specimen  has  ribs  on  the  last  dor- 
sal vertebra,  as  also  did  the  specimen  figured  by  Schmidt.  Neither 
Franque  nor  Shufeldt  found  such  ribs  in  the  specimens  investigated 
by  them. 

On  the  upper  and  lower  surfaces  of  each  of  the  free  pleuro- 
centra  of  the  tail,  in  a  line  on  each  side  with  the  bases  of  the 
arches,  are  found,  in  fresh  specimens,  slightly  projecting  masses  of 
cartilage.  Schmidt  describes  these  and  gives  figures  of  them  viewed 
externally  and  in  microscopic  section.  He  regards  them  as  rudiment- 
ary arches,  upper  and  lower,  belonging  to  the  intercalated  vertebral 
bodies.  Stannius  (58,  p.  21)  refers  to  these,  and  compares  them  to 
the  masses  of  cartilage  which  are  seen  between  the  true  vertebrae 
and  the  arches  resting  on  them.  But  Franque  had  observed  them 
still  earlier,  as  is  shown  in  the  paragraph  already  quoted  from  him. 

Schmidt  has  described  another  set  of  cartilages,  which,  he  claims, 
have  not  been  mentioned  by  other  writers.  These  are  said  to  be 
found  in  front  of  the  bases  of  the  upper  arches  of  the  dorsal  ver- 
tebrae, and  they  fill  up  partially  the  space  between  the  successive 
arches.  Schmidt  regards  these  cartilages  as  homologous  with  those 
just  described  as  occurring  on  the  upper  side  of  the  "  intercalated  " 
bodies  of  the  tail,  and  therefore  as  rudimentary  upper  arches.  I  will 
say  here  that  I  have  examined  these  masses  by  means  of  transverse 
and  longitiidin^.1  sections,  and  find  that  they  are  not  distinct  carti- 
lages, but  the  anterior  portions  of  the  masses  which  occur  between 
the  several  vertebral  bodies  and  their  neural  arches. 

There  is  another  system  of  cartilages  which  is  of  much  interest, 
and  which  has  received  little  attention.  These  are  found  on  the  under 
side  of  all  the  dorsal  vertebrae,  there  being  two  to  each  vertebra.  On 
most  of  the  vertebrae  these  two  cartilages  project  somewhat  beyond 
the  surface  of  the  bone  in  a  linear  form,  and  are  placed  one  on  each 
side  of  the  tract  occupied  by  the  dorsal  aorta.  In  the  dried  skeleton  they 


i2  FIELD  COLUMBIAN  MUSEUM — ZOOLOGY,  VOL.   i. 

show  themselves  as  two  linear  pits  running  parallel  with  each  other 
and  with  the  axis  of  the  vertebra.  In  the  more  anterior  vertebrae 
they  are  nearly  circular.  Here  they  lie  nearer  the  front  end  of  the 
vertebral  body  (Fig.  4).  In  the  succeeding  vertebrae  the  anterior 
ends  of  the  cartilages  come  close  to  the  anterior  ends  of  their  respec- 
tive centra,  but  become  gradually  more  extended  backward.  Finally, 
in  the  hinder  two-thirds  of  the  trunk  they  are  so  lengthened  as  to 
occupy  the  whole  of  the  length  of  the  centra  (Figs.  2  and  3). 
These  cartilages  are  found  even  on  the  vertebral  bodies  which  are  so 
closely  united  with  the  head.  They  appear  to  have  been  noticed 
only  by  Dr.  M.  Sagemehl  (54,  57)  who  observed  them  on  the  verte- 
brae at  the  hinder  end  of  the  skull  and  followed  them  backward  along 
the  vertebral  column.  He  states  that  in  young  individuals  these  car- 
tilages penetrate  deeply  into  the  substance  of  the  centra,  while  in 
•older  specimens  only  thin  plates  of  cartilage  can  be  recognized  rest- 
ing superficially  on  the  vertebrae.  He  enters  into  no  explanation  of 
these  structures.  They  will  engage  our  attention  later.  We  may, 
however,  note  here,  that  in  the  case  of  three  or  four  species  of  Amia 
described  by  Dr.  Joseph  Leidy  (44,  p.  185,  pi.  xxxii.)  from  the 
Bridger  Beds  of  the  Eocene  of  Utah,  there  occur  on  the  lower  side 
of  the  vertebral  body  a  pair  of  fossae,  which  occupy  exactly  the  posi- 
tion of  the  cartilages  in  Amia.  The  same  fossae  have  been  observed 
and  figured  by  Prof.  E.  D.  Cope  in  species  of  Pappichthys,  also  occur- 
ring in  the  Bridger  Beds  (17.  p.  56,  PI.  iii.).  They  are  spoken  of 
as  two  parallel  fissures  which  further  backward  become  oblong 
fossae,  and  again  near  the  caudal  vertebrae  are  narrowed.  Prof.  Cope 
further  says  that  in  the  caudal  vertebrae  these  fossae  are  as  well  devel- 
oped as  are  the  neurapophysial  pits,  and  are  much  like  them.  He 
evidently  had  in  mind  here  the  articulatory  surfaces  of  the  haemal 
arches,  which  are  very  different  things. 

The  structure  of  the  terminal  portion  of  the  vertebral  column 
has  been  more  or  less  accurately  described  by  Franque  (26),  Kolliker 
(43),  Wilder  (59),  and  Shufeldt  (57).  Of  these  accounts  it  seems  to 
me  that  that  of  Kolliker  is  the  most  complete  and  his  figures  the 
most  accurate.  Shufeldt  presents  an  original  figure  of  this  region,  but 
he  omits  a  representation  of  the  cartilaginous  elements,  and,  as  it 
appears  to  me,  of  some  of  the  bones.  Dr.  Wilder  had  not  seen  Kol- 
liker's  paper  when  he  wrote  his  notes,  and,  through  what  appears  to 
have  been  a  misunderstanding  of  Aug.  Dumeril's  language  (25,  ii. 
401)  he  ascribed  to  Kolliker  views  not  held  by  the  latter  author.  So 
far  as  they  bear  on  the  same  points,  Wilder' s  results  coincide  with 
those  of  Kolliker. 


OCT.  1895.  VERTEBRAL  COLUMN  OF  AMIA — HAY  13 

Kolliker's  figures  and  descriptions  cover  twelve  vertebral  bodies, 
the  prolongation  of  the  vertebral  axis  behind  these,  and  the  arches 
and  other  parts  connected  with  these  two  regions.  Of  the  centra 
described  and  figured,  the  anterior  seven  are  called  "complete,"  in- 
asmuch as  they  are  provided  with  fully  developed  neural  and  haemal 
arches.  The  last  five  are  "incomplete,"  that  is,  they  have  haemal 
arches  but  not  ossified  neural  arches.  Belonging  to  the  seven  com- 
plete vertebras  there  are,  however,  only  six  neural  arches,  since  the 
second  arch,  counting  from  before,  is  situated  over  the  articulation 
between  the  second  and  third  centra,  and  belongs  equally  to  both. 
As  was  first  shown  by  Franque  and  later  by  Kolliker,  the  so-called 
intercalated  vertebral  bodies  are  no  longer  developed  in  this  portion 
of  the  vertebral  column.  Shufeldt's  figure  represents  the  alternation 
of  pleurocentra  and  intercentra  as  ending  in  front  of  the  tenth  ver- 
tebra from  the  tip  of  the  ossified  part  of  the  vertebral  axis.  This 
failure  of  the  "intercalated"  centra  to  develop  is  only  a  part  of  the 
degeneration  which  has  affected  this  region  and  been  associated  with 
the  production  of  the  heterocercal  tail  of  Amia. 

In  the  case  of  three  specimens  examined  by  myself  I  find  that 
the  vertebra  called  by  Kolliker  the  last  complete  one,  being  the  last 
one  furnished  with  an  osseous  neural  spine,  shows  a  different  state  of 
affairs.  There  is  no  osseous  neural  arch,  but  there  are  two  cartilag- 
inous plates  present,  which  meet,  or  nearly  meet,  above  the 
spinal  cord.  These  are  also  segmented  off  from  the  cartilage 
which  represents  the  next  segment  behind.  Shufeldt  represents 
this  vertebra  as  having  a  neural  spine,  and  hence  we  may  conclude 
that  the  spine  is  sometimes  developed,  sometimes  not. 

As  Kolliker  has  shown,  the  haemal  arch  of  the  vertebra  just  men- 
tioned is  different  from  those  which  precede  it.  The  latter  all  have 
conspicuous  cartilaginous  bases,  one  on  each  side  of  the  haemal  canal, 
and,  as  shown  by  sections,  penetrating  to  the  center  of  the  vertebral 
body.  The  former  arch,  represented  by  a  haemal  spine,  or  hypural 
bone,  is  co-ossified  to  the  lower  side  of  the  corresponding  centrum. 

The  five  terminal  vertebrae  have  ossified  centra,  and  each  has  its 
own  haemal  arch,  but  there  are  no  distinct  neural  arches.  In  the 
place  of  these  there  is  a  continuous  band  of  cartilage  which  roofs  over 
the  spinal  canal,  and  is  prolonged  posteriorly  to  the  end  of  the  noto- 
chord,  some  distance  beyond  the  distal  ends  of  the  hypural  bones. 
The  last  five  vertebrae  are  more  or  less  reduced  in  size  as  we  proceed 
backward,  while  the  portion  of  the  vertebral  axis  represented  by 
them  is  turned  strongly  upward.  That  portion  of  the  continuous 
cartilage  which  overroofs  the  last  five  vertebrae  represents,  as  Kolli- 


14  FIELD  COLUMBIAN  MUSEUM — ZOOLOGY,  VOL.   i. 

ker  indicates,  the  neural  arches  of  these  vertebrae.  These  arches  have 
become  expanded  anterio-posteriorly  and  have  coalesced.  Belonging 
lo  each  of  these  arches  is  a  haemal  arch  in  the  form  of  a  hypural 
bone.  Each  is  co-ossified  with  the  under  side  of  its  proper  vertebra 
just  as  is  the  last  hypural  belonging  to  the  last  so-called  complete 
vertebra.  The  last  three  of  the  haemal  arches  are  directed  nearly 
horizontally  backward.  These  are  followed  by  two  other  similar 
bones,  which  Kolliker  says  belong  to  the  last  vertebra,  the  hinder- 
most  looking  like  a  continuation  of  the  vertebral  column.  On  this 
point  I  shall  have  something  to  say  when  I  come  to  speak  about  the 
microscopic  structure  of  these  parts. 

Lying  between  the  bone  last  mentioned  and  the  cartilage  which 
is  prolonged  behind  the  ossified  centra,  Kolliker  describes  another 
similar  bone  which  does  not  reach  the  last  centrum.  It  functions  as 
.a  ray-bearer,  and  doubtless  is  the  lower  arch  of  a  vertebra  which  has 
ceased  to  attain  development.  I  find  this  bone  in  two  specimens. 

Kolliker  describes  that  portion  of  the  cartilage  which  projects 
beyond  the  last  vertebral  body  as  consisting  of  a  tube  which  incloses 
the  spinal  cord,  or  its  representative.  On  the  underside  of  the  carti- 
laginous rod  is  a  furrow,  at  first  shallow,  and  in  this  lies  the  noto- 
chord. Posteriorly  the  furrow  deepens,  and  at  length,  near  the  ter- 
mination of  the  cartilage,  the  notochord  is  enveloped  in  the  substance 
of  the  cartilage.  Everywhere  there  is,  according  to  Kolliker,  a 
partition  of  cartilage  between  the  notochord  and  the  spinal  cord. 
This  matter  will  come  up  for  consideration  later.  Kolliker  regards 
the  extension  of  cartilage  behind  the  last  vertebra  as  representing 
not  only  the  upper  arches  but  also  the  continuation  of  the  vertebra] 
bodies.  It  thus  represents  a  cartilaginous  vertebral  column  ("eine 
ganze  knorpelige  Wirbelsaule  darstellt"). 

The  tail  of  Amia  has  not  attained  the  stage  of  complete  hetero- 
•cercality,  that  is,  it*s  not  hypocercal.  There  are  still  a  few  fin-rays 
lying  above  the  vertebral  axis.  Of  these  epural  fin-rays,  Kolliker 
figures  five,  all  unsegmented.  Shufeldt  figures  apparently  three, 
all  much  segmented.  The  specimens  which  I  have  examined  show 
three  rays,  only  the  most  posterior  being  segmented  sparingly.  Of 
epural  interspinous  bones,  Kolliker  figures  four,  the  most  posterior 
being  one  which  lies  closely  against  the  upper  side  of  the  prolonged 
cartilage.  Shufeldt  figures  six  interspinous  bones',  the  hindermost  of 
which  is  apparently  the  one  which  lies  close  to  the  rod  of  cartilage. 
This  series  of  bones,  as  shown  by  the  author  last  named,  completely 
fills  up  the  space  between  the  last  dorsal  ray  and  the  upper  border  of 
the  caudal  fin.  He  is  of  course  in  error  when  he  states  that  these 


OCT.  1895.  VERTEBRAL  COLUMN  OF  AMIA — HAY  15 

bones  have  not  been  previously  observed.  Shufeldt  remarks  (57,  ex- 
planation of  plate  ix.)  that  these  bones,  taken  in  connection  with  the 
free  spines  (interspinous  bones)  found  over  the  vertebrae  immediately 
behind  the  head,  suggest  that  in  the  early  ancestors  of  Amia  the  fin 
was  continuous  from  the  base  of  the  cranium  to  the  tail.  In  Oligo- 
plciirus,  of  the  Upper  Jura,  which  has  a  far  shorter  dorsal  fin,  there 
is  a  series  of  such  bones  occupying  the  whole  space  between  the  head 
and  the  dorsal  fin.  (Zittel,  60;  iii.  231.) 

Of  these  epural  interspinous  bones  I  have  found,  in  two  speci- 
mens examined,  also  four.  The  third  of  these  bones  is  in  close  rela- 
tion with  the  base  of  the  next  to  the  last  epural  fin-ray,  the  second  of 
those  found  by  me.  The  fourth  bone  is  closely  bound  to  the  upper 
surface  of  the  prolonged  cartilage.  Its  proximal  end  reaches  for* 
ward  so  as  to  overlap  somewhat  the  last  but  one  of  the  ossified  verte- 
bral centra.  The  distal  end  appears  to  be  embraced  by  the  lateral 
halves  of  the  hindermost  epural  fin-ray. 

2.       THE  MINUTE  STRUCTURE  OF  THE  VERTEBRAL  COLUMN. 

Kolliker  has  dealt  with  the  microscopical  structure  of  the  termi- 
nal portion  of  the  tail.  Schmidt  has  also  described  and  illustrated 
with  a  number  of  figures  some  points  in  the  finer  structure  of  the 
vertebral  column. 

In  all  the  vertebras  of  this  fish  the  bases  of  the  arches,  upper 
-and  lower,  come  into  contact  with  the  sheath  of  the  notochord.  \  In 
my  specimen,  12. 5 cm.  long,  these  bases  consist  of  clear  cartilage,  but 
at  the  inner  ends  of  the  bases  small  portions  of  the  cartilage  are  ab- 
sorbed. This  process  of  absorption  continues  as  the  individual 
increases  in  size,  until  probably  the  greater  part  of  the  cartilage  is 
removed.  While  this  is  going  on,  trabeculae  of  bone  are  depos- 
ited, which  look  exactly  like  the  bone  deposited  elsewhere  in  the  cen- 
trum; but  the  crust  of  bone  which  first  spread  over  the  base  of  the 
arches  serves  to  define  their  boundaries.  See  figures  i,  5,  6,  7. 

It  is  interesting  to  observe  that  in  the  case  of  the  simple  verte- 
brae, as  those,  of  the  dorsal  region,  the  cartilage  contained  in  the 
upper  arch  is  segmented  off  at  the  surface  of  the  centrum  from  the 
cartilage  enclosed  within  the  centrum;  while  the  cartilage  of  the 
arches  in  the  middle  of  the  tail  is  continuous  with  that  of  the  cen- 
trum. 

The  cartilages  which  have  already  been  referred  to  as  appearing 
in  pairs  on  the  underside  of  each  dorsal  vertebra,  may  be  now  more 
fully  described.  They  are  shown  in  figures  i,  5,  6.  As  seen  in 
longitudinal  section,  they  may  be  regarded  as  thin  trigtilanar  plates, 


16  FIELD  COLUMBIAN  MUSEUM — ZOOLOGY,  VOL.   i. 

whose  bases  are  seen  on  the  surface  of  each  of  the  vertebrae, 
while  their  apices  reach  usually  to  the  notochordal  sheath.  The  car- 
tilage appears  to  persist  even  in  adult  life.  It  is  ensheathed  in  a  thin 
layer  of  bone,  and  in  cross  sections  this  is  seen  to  extend  outward  as 
far  as  does  the  cartilage  itself.  Hence  when  the  cartilage  shrinks 
through  drying,  there  is  left  a  little  rim  of  bone  surrounding  the  pit. 
Inmost  of  the  trunk  region,  the  bases  of  these  cartilages  do  not  come 
into  contact  with  the  intravertebral  bases  of  the  transverse  processes 
(Fig.  i).  In  the  posterior  dorsal  region,  however,  where  the  pro- 
jesses  have  descended  considerably,  the  cartilages  in  question  come 
into  contact  with  the  intravertebral  bases  of  the  lower  arches, 
and  soon  have  the  appearance  of  being  suspended  from  their  lower, 
or  inner,  sides  (Fig.  5).  Toward  the  last  dorsal  vertebra  these 
cartilages,  which,  from  their  relation  to  the  aorta,  may  be  called  the 
aortal  supports,  become  shorter.  In  the  last  dorsal  vertebra  (Fig.  6) 
the  cartilage  is  short,  and  is  attached  to  the  intravertebral  basis  of  the 
haemal  arch  half-way  from  the  notochord  to  the  outer  surface  of  the 
vertebra.  In  the  vertebras  of  the  tail  the  cartilages  are  missing. 
There  is,  however,  in  my  younger  specimen,  what  seems  to  be  ves- 
tiges of  them  in  the  first  caudal  vertebra.  Nothing,  however,  can  be 
more  certain  than  that  the  lower  arches  of  the  trunk  are  bent  down 
to  form  the  arches  of  the  tail,  and  that  the  aortal  supports  have 
nothing  to  do  with  the  formation  of  the  caudal  haemal  arches.  In  the 
last  dorsal  vertebra  we  find,  at  the  anterior  end,  the  aortal  supports 
looking  somewhat  like  the  lower  arch-bases.  Further  back, 
however,  the  latter  come  into  view,  in  a  series  of  sections,  and 
the  aortal  supports  cling  to  their  inner  surfaces  (Fig.  6).  Figure 
7  shows  a  section  through  the  first  caudal.  The  bases  of  the  lower 
arches  are  seen  in  same  position  as  in  the  last  dorsal. 

The  origin  and  the  homology  of  these  aortal  supports  will  be  fur- 
ther considered  when  we  come  to  examine  younger  specimens.  In 
many,  if  not  most,  of  the  osseous  fishes,  there  is  to  be  found  on  the 
under  side  of  each  of  the  dorsal  vertebrae,  a  pair  of  bony  ridges,  one 
on  each  side  of  the  aorta.  To  these  ridges  the  aorta  appears  to  be 
suspended.  In  the  anterior  portion  of  the  vertebral  axis  of  Acipenser 
a  plate  of  cartilage  grows  downward  from  the  lower  edge  of  the  base 
of  each  half  of  the  haemal  arch,  and  gives  support  and  protection  to 
a  portion  of  the  aorta.  Further  back,  these  cartilaginous  plates  bend 
inward  towards  each  other,  and  finally  unite  below  the  aorta,  thus 
enclosing  it  in  a  canal.  It  appears  to  me  that  the  aortal  supports  of 
Amia  may  be  regarded  as  the  equivalents  of  those  cartilaginous  pro- 
cesses which  protect  the  aorta  in  Acipenser.  In  Amia  the  cartilages 


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AMI  A 


PLATE  I. 

Fig.     1.     Section  through  an  anterior  dorsal  vertebra  of  a  specimen  12.5  c.  ra  • 
long,  showing  the  three  pairs  of  cartilaginous  rays  penetrating  to  the  notochord,  viz., 
the  cartilages  which  support  the  bases  of  the  upper  arches,   the  bases  of  the   lower 
arches,  and  the  aortal  supports. 

Fig.  2.  Ventral  view  of  the  3(5th  dorsal  vertebra  of  adult  specimen,  showing 
especially  the  gaps  in  the  bone  which  are  occupied  by  the  cartilaginous  aortal  sup- 
ports. 

Fig.  3.     Ventral  view  of  13th  and  14th  dorsal  vertebrae  of  adult. 

Fig.  4.     Ventral  view  of  1st  and  2nd  dorsal  vertebrae  of  adult. 

Fig.  5.     Section  of  penultimate  dorsal  vertebra  of  specimen  12.5  c.  m.  long. 

Fig  6.  Section  of  last  dorsal  vertebra  of  same  specimen  as  the  last.  Taken 
near  the  middle  of  the  vertebral  centrum. 


FIELD  COLUMBIAN    MUSEUM 


ZOOLOGY.  PL. 


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.G 


AMI  A 


PLATE  II. 

Fig.  7.     Section  through  the  first  caudal  vertebra  of  same  specimen. 

Fig.  8.  Sagittal  section  through  the  axial  region  of  a  young  Amia,  15  mm.  long. 
Taken  just  behind  the  head.  Shows  the  bases  of  the  upper  arches  placed  between 
the  intercalated  cartilages,  which  themselves  rest  on  the  elastica  externa. 

Fig'  9.     Transverse  section  through  8th  dorsal  vertebra  of  Amia  27  mm.  long. 


FIELD  COLUMBIAN   MUSEUM 


ZOOLOGY.  PL.  II 


A.a, 


0.?H  iJe! 


B-MeisellitUwM. 


AMIA 


FIELD  COLUVHAK    MUSEUM  ZOOLOGY.  PL 


.III  3TAJCI 

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AND     ACiPENSER. 


PLATE  III. 

Fig.  10.  Longitudinal  section  through  the  axial  region  at  the  base  of  the  tail  of 
a  specimen  of  Amia  30  mm.  long.  Shows  especially,  on  the  right  hand,  the  upper 
and  the  lower  intercalated  cartilages;  on  the  left  hand,  the  interposition  of  the  upper 
intercalated  cartilages  between  the  bases  of  the  upper  arches  and  the  notochord; 
while  the  intercalated  cartilages  are  wanting  between  the  bases  of  the  lower  arches  on 
the  left  hand. 

Fig.  11.  Side  view  of  a  portion  of  the  dorsal  region  of  the  vertebral  column  of 
Adpenser.  Shows  bases  of  upper  and  lower  arches  and  the  cartilages  intercalated 
between  them  ;  also  between  the  two  series  of  arches  an  uncovered  portion  of  the 
notochord. 

Fig.  12.  Cross-section  through  a  posterior  dorsal  vertebra  of  an  Amia  23mm. 
Shows  especially  the  situation  of  the  earliest  points  of  ossification. 


FIELD  COLUMBIAN    MUSEUM 


ZOOLOGY.  PL.  III. 


O.P.H  del. 


not. 


B  Meisel  Mh  Bos'w 


AMIA     AND     ACIPENSER. 


OCT.  1895.  VERTEBRAL  COLUMN  OF  AMIA — HAY  17 

are  apparently  somewhat  more  independent  of  the  haemal  arches,  but 
there  seems  to  be  no  reason  why  this  condition  should  not  be  the  re- 
sult of  specialization. 

A  microscopical  examination  of  the  caudal  region  of  a  specimen 
about  1 2  smm.  in  length,  has  given  me  results  which  may  be  of  some 
value. 

The  last  but  one  of  the  "  complete"  vertebrae  is  in  all  respects 
similar  to  the  vertebrae  preceding  it.  Both  arches,  the  upper  and  the 
lower,  sit  upon  cartilaginous  bases,  and  these  latter  penetrate  close 
to  the  notochord.  The  next  vertebra,  like  the  corresponding  verte- 
bra in  each  of  the  two  specimens  microscopically  examined,  lacks  the 
neural  spine,  while  also  the  lateral  halves  of  the  neural  arch  appear 
not  to  meet  over  the  spinal  canal.  The  cartilages  on  which  the  neu- 
ral arch  is  based  reach  nearly  to  the  center  of  the  vertebra,  so  that 
on  the  upper  side  the  notochord  is  constricted,  just  as  in  the  case  of 
the  more  anterior  vertebrae.  The  haemal  arch,  on  the  contrary,  has 
no  such  broad  cartilaginous  bases,  although  its  proximal  end  contains  a 
nodule  of  cartilage.  The  lower  arms  of  the  cross  seen  in  cross-sections 
of  the  more  anterior  vertebras  are  here  wanting,  and  the  lower  side 
of  the  notochord  is  extremely  little  constricted.  The  ossified  hypural 
spine  is  consolidated  with  a  thin  shell  of  bone  which  forms  the  lower 
side  of  the  vertebral  centrum.  The  appearance  presented  suggests 
that  the  base  of  the  haemal  spine  has  originated  at  a  relatively  late 
period  in  the  development  of  the  individual,  so  that  it  has  not  stood 
in  the  way  of  the  growth  of  the  notochord. 

Giving  our  attention  to  the  five  vertebrae  which  follow  the  one 
just  described,  we  find  that  each  possesses  the  upper  arms  of  the  car- 
tilaginous cross  and  that  upon  the  ends  of  these  arms,  rest  the  edges 
of  the  strip  of  cartilage  which  roofs  over  this  part  of  the  spinal  canal ; 
just  as  the  neural  arches  of  the  more  anterior  vertebrae  rest  on  the 
upper  ends  of  the  cartilaginous  crosses  of  their  respective  vertebrae. 
Moreover,  that  part  of  this  roofing  cartilage  which  overlies  the  first  two 
of  these  last  five  vertebrae  is  almost  wholly  segmented  off  from  that 
behind  it  by  an  incision  which  begins  in  the  lower  border  and  runs 
upward.  This,  taken  in  connection  with  the  spineless  condition  of 
the  vertebra  just  preceding,  presents  a  gradual  transition  between 
the  normal  neural  arches  and  those  which  have  become  concrescent ; 
so  that  it  is  quite  certain  that  this  anterior  portion  of  the  prolonged 
cartilage  is  made  up  alone  of  the  neural  arches.  It  is  also  to  be  ob- 
served here  that  the  upper  side  of  the  notochord  has  suffered  con- 
striction at  the  points  touched  by  the  lower  ends  of  the  intravertebral 
cartilages. 


i8  FIELD  COLUMBIAN  MUSEUM — ZOOLOGY,   VOL.   i. 

The  five  hypural  bones  of  this  section  are  coossified  to  their  re- 
spective vertebrae  in  the  same  way  as  has  been  described  in  the  case 
of  the  vertebra  immediately  preceding.  No  cartilage  is  present,  but 
the  lower  surface  of  the  vertebral  centrum  is  composed  of  a  thin 
crust  of  bone,  possibly  of  cartilaginous  origin,  and  to  this  is  coossi- 
fied the  corresponding  hypural.  The  notochord  enclosed  by  these  cen- 
tra has,  on  the  underside,  undergone  little  constriction. 

My  longitudinal  sections  do  not  confirm  Kolliker's  view  that  the 
next  two  hypurals  are  attached  to  the  terminal  centrum  of  the  tail. 
While  the  base  of  the  first  of  these  hypurals  does  come  close  up  to  the 
hinder  border  of  the  last  centrum,  it  is  entirely  distinct  from  the  lat- 
ter. At  the  same  time  its  proximal  end  reaches  backward  and  sup- 
ports its  own  portion  of  the  notochord.  The  next  hypural  is  in  its 
turn  brought  into  contact  with  the  notochordal  sheath  still  further 
back,  and  is  not  at  all  coossified  with  the  last  developed  centrum. 
An  examination  of  the  next  to  the  last  hypural  bone  shows  that  its 
base  closely  resembles  that  of  the  vertebrae  in  front;  since  there  is, 
next  to  the  notochordal  sheath,  a  layer  of  ossified  cartilage.  We 
have  therefore  some  reason  to  believe  that  the  base  of  this  hypural 
has  become  coossified  with  the  lower  portion  (hypocentrum)  of  an 
imperfectly  developed  vertebral  centrum.  The  base  of  the  last 
hypural  is  also  somewhat  expanded,  and  this  expansion  possibly  rep- 
resents another  rudimentary  centrum.  It  is  not  at  all  improbable  that 
at  a  later  period  of  life  these  hypurals  coossify  by  their  proximal  ends 
jto  the  hindermost  vertebral  centrum,  so  as  to  produce  the  condition 
described  by  Kolliker. 

It  is  interesting  to  note  that  the  notochord  over  these  two  hypu- 
rals just  described,  has  suffered  slight  constriction,  as  if  in  sympathy 
with  the  effort  to  develop  additional  centra. 

In  my  sagittal  sections  I  find,  in  place  of  the  staff-like  bone 
which  is  sometimes  seen  above  the  last  described  hypural,  and  which 
is  itself  undoubtedly  but  another  hypural,  a  row  of  three  cartilages. 
The  two  most  anterior  of  these  nodules  of  cartilage  are  covered  with 
a  layer  of  bone. 

Turning  our  attention  now  to  the  band  or  rod  of  cartilage  which 
is  prolonged  beyond  the  ossified  vertebral  column  and  ends  between 
the  lateral  halves  of  the  twenty-first  caudal  ray,  we  find  that  Kolli- 
ker, as  already  stated,  regards  it  as  representing  not  only  the  upper 
arches,  but  also  the  continuation  of  the  vertebral  centra.  According 
to  Kolliker's  description  and  figures,  the  cartilage  under  considera- 
tion forms,  for  some  distance  beyond  the  last  vertebral  body,  a  com- 
plete tube,  which  encloses  the  spinal  cord,  or  its  representative.  On 


OCT.  1895.  VERTEBRAL  COLUMN  OF  AMIA — HAY  19 

the  underside  of  this  tube  is  a  furrow,  at  first  shallow,  but  growing 
deeper  towards  the  hinder  end.  In  this  furrow  runs  the  notochord. 
Near  the  tip  of  the  cartilage  the  edges  of  the  furrow  meet  and  co- 
alesce below  the  notochord.  Kolliker's  figures  show  a  relatively 
thick  wall  of  cartilage  everywhere  between  the  spinal  cord  and  the 
notochord.  In  my  sections  there  is,  on  the  contrary,  from  the  last 
•ossified  centrum  to  the  tip  of  the  notochord,  no  cartilage  between 
the  latter  and  the  spinal  cord.  The  narrow  space  between  them  is 
•occupied  by  loose  connective  tissue  and  blood-vessels.  The  lower 
borders  of  the  cartilage  incline  inward  between  the  two  structures, 
but  do  not  meet.  The  condition  described  by  Kolliker  is  probably 
.attained  at  a  more  advanced  age.  Farther  back,  at  a  point  some  dis- 
tance behind  the  distal  ends  of  the  hypurals,  the  cartilage  gradu- 
ally spreads  downward  over  the  sides  of  the  notochord,  and  finally 
completely  encloses  it.  Under  these  circumstances  it  appears  to  me 
probable  that  this  whole  strip  of  cartilage  has  resulted  from  the 
•downward  extension  of  coalesced  neural  arches,  and  none  of  it  from 
the  lower  arches.  It  is  also  interesting  to  observe  that  there  are  in 
this  portion  of  the  terminal  cartilage  seven  shallow  nicks  along  its 
lower  border.  These  suggest  a  partial  separation  into  distinct  seg- 
ments. 

The  notochord  in  this  region  has  a  thick  cuticular  sheath,  outside 
of  which  is  to  be  distinctly  seen  the  elastica  externa.  In  my  sections 
-of  the  hinder  tail  region  of  the  specimen  125111111.  long,  the  noto- 
chordal  sheath  is  far  from  having  a  structureless  appearance.  Espec- 
ially along  the  portion  where  the  incomplete  vertebrae  are  developed, 
but  also  further  backward,  the  sheath  is  traversed  from  elastica  to 
notochord  by  lines,  or  fibers,  of  some  substance  which  stains  deeply 
with  carmine.  Where  the  notochord  is  constricted  by  the  upper  por- 
tion of  the  incomplete  vertebrae,  these  fibres  appear  to  start  from  the 
lower  surface  of  the  elastica.  Here  they  are  so  close-set  as  to  resem- 
ble the  hairs  of  a  brush,  but  as  they  approach  the  inner  surface  of  the 
sheath  they  become  finer  and  less  numerous. 

In  this  same  region  the  inner  cuticular  sheath  has  undergone 
another  modification,  to  which  I  will  call  attention.  Where  the  last  six 
vertebrae  of  the  upturned  portion  of  the  tail  have  constricted  the 
notochord,  especially  on  the  upper  side,  we  find  that  the  outer  half, 
or  somewhat  less,  of  the  cuticular  sheath  stains  deeply.  One  is 
reminded  of  the  modification  suffered  by  the  sheath  of  the  notochord 
of  Lepisosteus,  as  described  by  Balf our  and  Parker  (4,  vol.  i,  781; 
vol.  iv.,  pi.  41  (Fig.  69).  InAmia,  however,  the  pulley-like  band  so 
modified  does  not  extend  far  forward  and  backward  beyond  the 


20  FIELD  COLUMBIAN  MUSEUM — ZOOLOGY,  VOL.    i. 

most  constricted  portion  of  the  centrum.  In  Lepisosteus  it  extends- 
in  each  direction  to  the  end  of  the  centrum.  In  Amia  the  fibres- 
described  in  the  preceding  paragraph  appear  to  pass  right  through 
the  modified  band  of  the  sheath. 

3. DISCUSSION  OF  THE  VERTEBRAL  COLUMN  OF  FOSSIL  FISHES. 

Having  now  considered  the  structure  of  the  vertebral  column  of 
the  living  Amia,  it  is  proper  to  determine  what  light  we  may  obtain 
regarding  its  peculiarities  by  a  consideration  of  such  fossil  forms  as 
may  be  related  to  it.  For  a  presentation  of  the  facts  relating  to  the 
Amioid  fishes  the  reader  is  referred  to  Dr.  Zittel's  "  Handbuch  der 
Palseontologie, "  vol.  iii.  Through  Amia,  Eurycornms,  Callopterus, 
Caturus,  and  related  genera,  we  are  apparently  led  back  to  more  and 
more  primitive  arrangements.  From  a  study  of  these  forms  attempts 
have  been  made  to  reach  an  explanation  of  the  mode  of  development 
of  the  vertebrae  of  these  fishes.  That  adopted  by  Dr.  Zittel  may  be 
thus  stated.  The  hypocentrum  (originally  of  two  lateral  halves)  is 
developed  on  the  lower  side  of  the  notochord  in  each  myomere,  and 
supports  the  lower  arch.  On  the  upper  side  of  the  notochord  are  devel- 
oped two  pleurocentral  plates,  which  may  also  become  consolidated 
into  one  piece.  Such  an  arrangement  may  be  found  in  Caturus.  In 
a  more  advanced  stage  of  development  the  hypocentrum  grows  fur- 
ther upward  on  the  sides  of  the  notochord,  while  the  extremities  of 
the  pleurocentrum  grow  downward.  The  borders  of  the  two  ele- 
ments may  at  length  come  into  contact,  and  thus  cover  in  the  whole 
surface  of  the  notochord.  Such  a  condition  may  be  seen  in  some  por- 
tions of  the  vertebral  column  of  Caturus  and  in  that  of  Callopterus. 
Further  growth  of  the  plates  results  finally  in  the  upper  ends  of  the 
hypocentrum  meeting  above  the  notochord,  and  thus  forming  a  com- 
plete ring.  In  a  similar  way,  the  pleurocentrum  of  each  myomere 
forms  another  ring.  We  find  such  rings  in  their  complete  develop- 
ment in  the  middle  region  of  the  tail  of  Amia. 

On  the  other  hand,  Ludwig  Schmidt  appears  to  regard  the  two 
rings  in  each  myomere  as  the  primitive  condition,  and  each  of  these 
as  a  distinct  vertebral  centrum,  the  one  with,  the  other  without, 
neural  arches.  As  to  the  manner  of  development  of  the  vertebral 
centra  of  the  dorsal  region,  Schmidt  presents  two  contradictor}7  views. 
He  at  first  states  that  these  vertebrae  must  be  regarded  as  resulting 
from  the  coalescence  of  two  such  vertebras  as  are  found  in  each  myo- 
mere of  the  tail  (56,  pp.  755  and  760).  And  he  presents  as  evi- 
dences and  illustration  of  this  fusion  the  varying  number  of  com- 
plete vertebrae  in  the  anterior  tail  region  and  the  occasional  fusion. 


OCT.  1895.  VERTEBRAL  COLUMN  OF  AMIA — HAY  21 

of  the  two  centra  in  the  middle  tail  region.  On  another  page  of  his 
paper,  when  Schmidt  comes  to  consider  the  fossil  forms  with  rhachi- 
tomous  vertebrae,  such  as  Eurycormus  and  Euthynotus,  he  explains 
these  structures  on  the  hypothesis  that,  starting  with  the  two  rings  in 
each  myomere  throughout  the  body,  the  hypocentrum  has  grown  at 
the  expense  of  the  pleurocentrum.  The  latter  becomes  reduced  in 
size  and  is  confined  to  the  upper  side  of  the  notochord.  Eurycormus 
furnishes  one  stage  ;  Euthynotus  a  more  advanced  one.  At  length 
the  pleurocentrum  becomes  a  mere  rudiment ;  and  in  Amia,  the  last 
of  the  series,  Schmidt  finds  the  pleurocentrum  represented  by  only 
the  small  masses  of  cartilage,  "the  rudimentary  upper  arches,,"  alleged 
to  lie  in  front  of  the  bases  of  the  developed  upper  arches.  Of  course, 
one  or  the  other,  or  both,  of  these  explanations  must  be  wrong ;  and 
neither  of  them  explains  the  arrangement  found  in  Caturus,  as  is 
admitted  by  Schmidt.  On  the  other  hand,  the  theory  that  the  rings 
have  resulted  from  the  growth  of  the  pleuro-and  hypocentral  plates, 
seems  capable  of  explaining  all  the  known  facts. 

Having  considered  the  mode  of  development  of  the  vertebrae  of 
the  Amioidei,  it  may  be  profitable  to  inquire  whether  or  not  any 
other  groups  of  fishes  have  possessed  similar  vertebras.  The  so- 
called  Ganoids  first  claim  our  attention. 

Our  modern  species  of  Lepisosteus  show  no  indications  in  their 
adult  condition  of  the  presence  of  pleuro-and  hypocentra.  But  Aspi- 
dorhynchus,  a  member  of  the  Rhynchodontidae,  had  dorsal  vertebrae 
•composed  evidently  of  two  portions.  These  formed  rings,  which 
were  divided  along  the  sides  by  sutures.  This  being  true  of  the  dorsal 
region,  we  can  hardly  floubt  that  the  caudal  vertebrae  also  originated 
from  once  distinct  pleuro-and  hypocentra.  The  tubular  vertebrae  of 
Belonorhynchus,  too,  must  have  had  a  similar  origin. 

In  the  family  Macrosemiidae,  Cope  ^Saurodontidae,  Zittel)  some 
genera  have  simple  tubular  vertebrae.  Others,  as  Eugnathus;  have 
the  vertebrae  composed  each  of  two  distinct  pieces.  The  species  of 
Pholidophorus  sometimes  possess  undivided  vertebrae,  but  usually  the 
centra  are  made  up  of  pleurocentra  and  hypocentra  (Zittel,  60,  p. 
315).  In  the  tail  these  two  pieces  stand  nearly  opposite  each  other 
and  form  a  bony  sheath  on  which  rest  the  upper  and  the  lower 
arches.  It  seems  quite  improbable  that  the  closely  related  genera 
fropterus  and  Histionotus  should  have  developed  vertebrae  in  an  en- 
tirely different  way. 

Little  is  known  concerning  the  state  of  the  vertebral  column  of 
the  Sphaerodontidae  and  the  Stylodontidae.  At  any  rate,  the  ossifica- 
tions were  feeble.  Tctragonolepis  is  said  to  have  had  ring- like  vertebrae. 


22  FIELD  COLUMBIAN  MUSEUM — ZOOLOGY,  VOL.   i. 

Dapedius  is  regarded  as  having  possessed  composite  vertebrae.  These 
meager  accounts  of  the  vertebral  structures  of  these  fishes  make  it 
probable  that  all  the  species  of  the  families,  so  far  as  they  possessed 
anything  representing  vertebral  centers,  had  the  two  elements,  pleu- 
rocentra  and  hypocentra.  And  the  same  having  been  shown  to  be 
true,  or  highly  probable,  of  every  family  of  the  order  Lepisostei, 
we  are,  I  think,  justified  in  reaching  the  conclusion  that  whenever 
ossification  of  the  vertebral  column  has  begun  in  members  of  this 
group,  it  has  been  through  the  formation  in  each  somite  of  a  lower 
piece  or  pieces,  on  which  rest  the  lateral  halves  of  the  haemal  arch ; 
while  on  the  upper  side  of  the  notochord  upper  pieces  of  bone  have 
been  deposited  in  the  region  of  the  bases  of  the  upper  arch ;  that  is, 
pleurocentra  and  hypocentra  are  normally  constituents  of  the  ver- 
tebral centrum. 

Of  the  condition  of  the  ancient  Crossopterygia,  as  regards  the 
vertebral  column,  we  have  little  knowledge.  Prof.  Cope  (15,  p.  19} 
states  that  in  Ectosteorhachis  (Megalichthys)  the  vertebrae  are  repre- 
sented by  annular  ossifications  resembling  those  of  Cricotus.  There 
appears,  however,  to  be  only  a  single  ring  in  each  myomere. 

From  the  foregoing  survey  of  the  condition  of  the  vertebral 
column  in  the  different  families  of  the  so-called  Ganoids,  one  may 
easily  become  convinced  that  originally  the  ossified  vertebral  centra 
of  all  the  species  that  possessed  such  were  composite  in  their  struc- 
ture; that  is,  each  centrum  included  in  its  composition  a  pleurocen- 
trum  and  a  hypocentrum.  Each  of  these  two  elements  was  doubtless 
itself,  at  an  earlier  period  of  its  history,  double.  If  the  centrum  is 
in  any  given  case  simple  in  structure,  this  has  probably  resulted  from 
the  coalescence  at  some  time  in  the  animal's  life  of  the  two  elements, 
or  possibly  sometimes  from  the  suppression  of  one  of  them.  If  we 
find  in  one  fish  the  notochord  surrounded  in  one  portion  of  the  body 
by  a  solid  vertebral  body,  and  in  another  portion  by  two  complete, 
but  distinct,  rings;  or  in  another  fish  the  notochord  in  one  region 
protected  by  pleurocentra  and  hypocentra,  while  in  another  region 
there  are  mere  rings,  it  appears  quite  improbable  that  these  different 
structures  have  no  genetic  connection.  It  is  equally  improbable  that 
in  species  of  the  same  family,  or  of  closely  related  families,  the  ver- 
tebral centers  originated  sometimes  as  mere  tubular  incrustations  of 
the  notochord,  sometimes  as  double  rings,  and  sometimes  as  pleuro- 
and  hypocentra.  Some  one  of  these  structures  must  have  been 
the  fundamental  one ;  and  if  so,  then  the  elements  which  have  been 
called  pleuro-and  hypocentra  must  be  regarded  as  the  most  primitive. 

To  what  extent  do  the  conclusions  we  have  reached  apply  to  the 
fishes  which  we  call  the  Teleostei  ? 


OCT.  1895.  VERTEBRAL  COLUMN  OF  AMIA — HAY  23 

By  the  consent  of  perhaps  all  modern  ichthyologists,  the  relation- 
ships of  the  Ganoids  and  the  Teleosts  are  very  close.  Dr.  Gill  (31) 
regards  the  two  groups  as  distinct  subclasses,  but  admits  that  in  some 
of  their  members  they  approach  closely.  Liitken  (46)  excludes  from 
the  Ganoids  large  groups  which  have  been  held  to  belong  there. 
Among  these  excluded  forms  are  the  Amioidei.  Others  abandon  the 
conception  of  the  Ganoids  as  forming  a  distinct  group.  Cope  forms 
of  the  bony  fishes,  and  some  of  the  Ganoids,  his  subclass  Actinopteri. 
It  is  hardly  open  to  doubt  that  the  Teleosts  have  descended  from  more 
or  fewer  of  the  families  of  ancient  Ganoids.  The  Halecomorphi  are 
intimately  related  to  the  Isospondyli,  and  have  probably  furnished 
the  ancestors  of  the  latter.  Hence  we  might  reasonably  expect  to 
find  in  some  of  the  recent  or  fossil  Teleosts,  in  the  stricter  sense, 
traces  of  the  composite  nature  of  the  vertebral  centra.  And  in  fact 
Prof.  Cope  (22)  expresses  the  opinion  that  the  fossil  genera  which 
possess  annular  vertebrae,  as  Aspidorhynchus,  should  be  assigned  to 
Isospondyli.  According  to  the  views  of  Liitken,  most  of  the  genera 
which  display  pleuro-and  hypocentra  would  be  thrown  among  the 
Teleosts.  The  Hoplopleuridae,  whose  members  range  through  the 
Mesozoic,  are  now  usually  assigned  to  the  Teleost  series.  In  some  of 
these  the  vertebral  column  is  imperfectly  or  not  at  all  ossified.  Be- 
lonorhynchus  has  feebly  ossified  vertebrae.  The  vertebral  elements 
appear  as  small  ossifications  at  the  bases  of  the  arches,  and  are  prob- 
ably to  be  regarded  as  pleuro-and  hypocentra.  Deecke  (24,  p.  131) 
points  out  the  close  resemblance  of  this  fish  to  Be/one  belone,  living 
now  in  the  Atlantic.  He  states  that  if  the  vertebral  column-of  Bel- 
onorhynchus  were  ossified  it  would  be  difficult  to  distinguish  the  two 
genera.  We  are  therefore  justified  in  expecting  that  our  living 
Teleosts  will  in  some  way  display  in  their  vertebral  structure  the 
existence  of  the  elements  which  we  have  found  in  so  many  of  the 
Ganoids.  Nevertheless,  we  are  not  yet  in  a  condition  to  demonstrate 
the  presence  of  such  elements.  The  vertebrae  of  our  fishes  have  not 
yet  been  investigated  sufficiently  from  this  point  of  view  to  enable 
us  to  speak  with  definiteness. 

It  is,  of  course,  entirely  possible  that  in  the  lapse  of  ages  one  or 
the  other  of  the  elements  of  the  vertebral  centrum  of  the  ancient 
fishes  has  entirely  disappeared,  while  the  other  remains  as  its  sole 
constituent.  And  this  is  what  Prof.  Cope  appears  to  believe  has  hap- 
pened. He  says  (22,  1019) :  "  The  so-called  centra  of  fishes  are  inter- 
centra  [hypocentra],  as  in  the  Batrachia."  This  opinion  may  be  cor- 
rect, but  the  grounds  on  which  it  appears  to  have  been  based  seem  to 
afford  it  insufficient  support.  "  The  descriptions  and  figures  of  Prof. 


24  FIELD  COLUMBIAN  MUSEUM — ZOOLOGY,  VOL.   i. 

Zittel  render  it  perfectly  clear  that  the  fishes  rarely  develop  complete 
vertebral  centra  [pleurocentra],  the  order  Halecomorphi  being  the 
only  example."  On  the  contrary  many  genera  belonging  to  a 
mimber  of  families  are  mentioned  by  Prof.  Zittel  as  possessing  pleu- 
centra  and  hypocentra. 

4.       DISCUSSION  OF  THE  VERTEBRAL  COLUMN  OF  THE  HIGHER 
VERTEBRATA. 

But  the  Ganoid  and  Teleost  fishes  are  not  the  only  vertebrates 
which  manifest  in  their  vertebral  centra  the  possession  of  the  ele- 
ments which  we  have  found  so  well  developed  in  the  vertebrae  of  the 
Amioid  fishes.  Hermann  von  Meyer  was  the  first  to  point  out  that 
the  vertebrae  of  the  fossil  Archegosaurus,  among  the  Amphibians, 
were  each  made  up  of  a  numher  of  distinc  t  pieces.  This  genus,  and 
others  closely  related  to  it,  show  indeed  a  remarkable  resemblance  in 
the  structure  of  their  vertebrae  to  the  fishes  related  to  Amia,  espec 
iaily  to  Caturus.  Others  again,  as  Cricotus  and  Diplovertebron,  have 
the  vertebrae  of  at  least  the  tail  constructed  exactly  like  the  vertebrae 
of  the  middle  portion  of  the  tail  of  Amia.  Some  other  fossil  genera, 
as  Mastodonsaurus,  usually  have  solidly  ossified  vertebrae,  but  Von 
Meyer  has  shown  that  such  vertebrae  may,  during  the  youth  of  the 
animal,  have  the  rhachitomous  structure  of  Archegosaurus.  Some  spe- 
cies, again,  as  those  classified  as  Lepospondyli,  had  simple  tubular 
vertebrae ;  but  in  closely  related  genera,  such  vertebrae  consisted  each 
of  a  right  and  left  half,  the  two  meeting  by  a  suture  along  the  dorsal 
and  ventral  sides  of  the  notochord.  Whether  in  such  cases  we  have 
two  pleurocentra  or  two  hypocentra,  or  the  two  elements  coalesced, 
it  may  yet  be  impossible  to  say.  Cope  holds  the  view  that  the  verte- 
brae of  modern  Amphibians  consist  only  of  hypocentra.  This  view 
will  be  discussed  further  on. 

On  the  other  hand  it  has  been  shown  by  Cope,  Albrecht,  Dollo 
and  Baur,  that  the  vertebral  centra  of  the  reptiles,  birds  and  ani- 
jnals  are  really  pleurocentra,  while  the  hypocentra  appear  only 
occasionally  in  reptiles,  especially  as  " subvertebral  wedge-bones," 
and  in  all  Amniota  as  the  "  body  "  of  the  atlas. 

The  finding  of  the  elements  pleurocentra  and  hypocentra  in  the 
vertebral  column  of  so  many  of  the  osseous  fishes,  the  amphibians, 
and  the  Amniota  may  well  lead  us  to  suspect  that  future  investigations 
will  reveal  a  still  more  general  participation  by  them  in  the  structure 
of  the  vertebral  column.  Such  investigations  may  further  prove  to 
what  extent  these  elements  enter  into  the  constitution  of  the  primi- 
tive vertebra  from  which  all  others  have  been  derived. 


OCT.  1895.  VERTEBRAL  COLUMN  OF  AMIA — HAY  25 

5.     THE  ORIGIN  AND  DEVELOPMENT  OF  THE  VERTEBRAE  OF  AMIA  DURING 

ITS  EARLY  STAGES. 

Since  my  results  obtained  from  the  study  of  adult  specimens 
have  been  put  in  practically  the  form  presented  above  to  the  reader, 
I  have  had  the  good  fortune  to  acquire  a  considerable  amount  of  lar- 
val and  young  material.  Some  of  this,  consisting  of  larvae  from  10 
to  i5mm.  in  length,  was  received  from  Dr.J.  E.  Reighard,  of  the  Uni- 
versity of  Michigan,  through  the  kind  offices  of  Dr.  Eycleshymer,  of 
the  University  of  Chicago.  For  the  possession  of  the  young  of  larger 
growth,  varying  from  23  to  44mm.,  I  am  indebted  to  Dr.  S.  A. 
Forbes,  of  the  University  of  Illinois,  and  his  assistant,  Prof.  Frank 
Smith.  The  University  of  Illinois  supports  a  biological  station  on 
the  Illinois  river  at  Havana;  and  it  was  here  that  Prof.  Smith  secured 
the  materials  sent  me.  As  a  result  of  a  study  of  the  young  of  Amia, 
I  am  able  to  throw  some  light  on  the  development  of  its  vertebral 
•column,  and  that  of  fishes  in  general. 

I  have  prepared  transverse  and  sagittal  sections  of  specimens 
lomm.  in  length.  An  enlarged  figure  of  a  specimen  of  this  length 
may  be  found  on  PI.  xxx.  of  Mr.  Allis's  paper  on  Amia  (i.)  In 
specimens  of  this  size  the  notochord  is  already  vacuolated.  The 
walls  of  the  vacuoles  stain  deeply  with  carmine,  but  not,  at  least  for 
me,  with  hsematoxylin.  Peripherally  they  pass  into  a  layer  resem- 
bling in  every  way  themselves,  but  thicker.  The  thickness  of  this 
external  layer  I  make  to  be  about  .oo66mm.  but  it  is  thicker  where 
the  vacuole  walls  enter  it.  It  apparently  represents  the  epithelial 
layer,  which  is  seen  at  a  later  stage,  but  I  find  in  it  no  traces  of  nu- 
clei, or  little  else  to  suggest  the  presence  of  cells.  Outside  of  it  lies 
a  highly  refractive,  extremely  thin  layer,  one  of  the  sheaths  of  the 
notoehord. 

Anteriorly  the  pointed  end  of  the  notochord  is  buried  in  the' con- 
nective tissue  closing  in  the  pituitary  space,  but  the  greater  portion 
of  the  cranial  division  is  enclosed  in  the  well  developed  cartilage  at 
the  base  of  the  skull.  This  cartilage  may  be  followed  backward,  in 
longitudinal  sections,  into  the  two  ridges  of  the  skeletogenous  tissues 
which  give  origin  to  the  upper  arches.  The  specimens  of  the  length 
being  considered  do  not  all  appear  to  be  in  the  same  stage  of  devel- 
opment. In  one  examined  the  most  anterior  upper  arches  consist  of 
[hyaline  cartilage.  In  another,  the  cartilage  at  the  base  of  the  skull 
passes  insensibly  into  procartilage  in  the  region  of  the  neural  arches. 
In  the  intervals  between  the  nerve  roots  may  be  seen  the  bases  of  the 
upper  arches,  distinguished  apparently  only  by  being  slightly  more 


26  FIELD  COLUMBIAN  MUSEUM — ZOOLOGY,  VOL.   i. 

condensed  than  the  tissues  which  lie  between  the  arches.  On  the 
lower  side  of  the  notochord  there  may  be  seen  at  intervals,  in  sagittal 
sections  of  the  more  advanced  lomm.  specimen,  little  masses  of  more 
dense,  more  deeply  staining  tissues,  the  beginning  of  the  lower 
arches.  In  cross  sections  these  may  be  traced  from  the  lower  outer 
side  of  the  notochord  downward  to  near  the  aorta,  their  lower  ends 
staining  a  little  more  deeply  in  haematoxylin.  In  the  less  advanced 
specimens  the  indications  of  the  arches,  upper  and  lower,  fade  out 
posteriorly ;  but  in  other  specimens  they  may  be  followed  into  the 
tail,  where  also  the  cartilage  becomes  better  differentiated.  Here 
the  lower  arches  may  be  seen  to  extend  down  the  sides  of  the  aorta 
and  pass  into  the  indifferent  tissue  which  surrounds  the  caudal  vein. 
The  upper  arches,  however,  have  become  very  short,  mere  cartilagi- 
nous papillae  at  the  sides  of  the  spinal  marrow. 

When  we  come  to  examine  specimens  having  a  length  of  i5mm. 
we  are  able  to  observe  a  number  of  important  changes  in  the  axial 
structures.  The  notochord  has  attained  a  diameter  of  about  .3mm. 
There  is  present  a  distinct  cuticular  sheath,  the  thickness  of  which  I 
make  .0033111111.  Outside  of  this  is  an  extremely  thin,  but  distinct, 
membrana  elastica.  Lying  within  the  cuticular  sheath,  and  surround- 
ing the  notochord  there  is  present  a  very  distinct  epithelial  layer. 
The  nuclei  of  the  cells  stain  deeply,  and  the  whole  layer  has  a  thick- 
ness of  about  .oo66mm.  How  this  layer  of  cells  originates  I  am  tin- 
able  to  say.  I  find  no  traces  of  it  in  a  specimen  i2mm.  in  length, 
except  it  be  the  already  described  cell-less  layer  just  inside  the  cuti- 
cular sheath.  Scheele  describes  and  figures  a  distinct  epithelial 
layer  as  existing  in  the  Trout  (55).  Goette  has  denied  the  exist- 
ence of  such  a  structure,  but  it  has  been  demonstrated  by  a  number 
of  competent  observers,  as  Gegenbaur,  Grassi,  etc. 

In  the  anterior  dorsal  region  the  upper  arches  rise  two-thirds  the 
height  of  the  spinal  cord,  passing  above  into  the  delicate  connective 
tissue  which  closes  in  the  latter  organ.  In  the  posterior  region  they 
are  very  short.  When  sagittal  sections  of  this  length  are  examined, 
we  find  that  in  the  anterior  region  some  new  elements  are  beginning 
to  show  themselves.  These  are  small  masses  of  incipient  cartilage, 
which  are  placed  immediately  in  front  of  the  bases  of  the  upper 
arches  (Fig.  8).  Whether  or  not  these  masses  are  ever  at  any 
time  united  with  the  bases  of  the  arches  by  continuous  cartilage, 
incipient  or  well  developed,  I  find  myself  unable  to  say  definitely.  In 
nearly  all  cases  there  may  be  seen  at  least  a  narrow  line  of  connective 
tissue  cells  surrounding  each  little  mass  and  cutting  it  off  from  the 
bases  immediately  in  front  and  behind.  But  occasionally,  both  while 


OCT.  1895.  VERTEBRAL  COLUMN  OF  AMIA — HAY  27 

the  cartilage  of  the  mass  is  in  the  undifferentiated  condition  and 
when  it  has  become  quite  hyaline,  a  section  may  be  found  in  which 
the  bases  and  the  intermediate  masses  appear  to  be  quite  continuous. 
These  masses  are,  as  is  to  be  expected,  best  developed  in  front,  and 
become,  in  this  stage,  very  obscure  about  the  middle  of  the  back. 
They  rest  immediately  on  the  elastica,  while  the  bases  of  the  arches- 
seem  to  have  been  crowded  upward  out  of  contact  with  it.  If  these 
little  cartilages  just  described  are  ever  actually  continuous  with  the 
bases  of  the  arches  immediately  before  and  behind  them,  they  cer- 
tainly become  first  cut  off  from  the  bases  just  in  front,  and  later  from 
the  bases  immediately  behind  them. 

In  the  region  of  the  tail,  masses  of  cells  suggesting  the  early 
stage  of  cartilage  are  seen  to  lie  between  the  bases  of  the  successive 
half-arches,  and  often  they  cannot  be  sharply  separated  from  the  ad- 
joining arch  bases.  This  applies  both  to  the  upper  and  the  lower  sides. 
of  the  notochord.  While  we  may  be  somewhat  uncertain  whether 
or  not  these  newly  appearing  masses  of  cartilage  have  a  direct  con- 
nection at  any  time  with  the  bases  of  the  arches,  this  much  is  very 
certain :  there  is  never  at  any  stage  a  contimiation  of  the  cartilage 
of  the  bases,  or  of  the  intermediate  masses  of  one  side,  across  the  noto- 
chord to  those  of  the  other  side.  Nor  have  I  found  anywhere  that 
the  cartilage  of  the  upper  arches  is  continuous  with  that  of  the  lower 
arches.  Hence  there  is  nothing  resembling  a  tube  of  cartilage  en~ 
closing  the  notochord. 

In  the  anterior  portion  of  the  body  the  cartilages  which  repre- 
sent the  lower  arches  have  not  changed  greatly  from  their  earlier 
condition.  The  cartilage  is  better  differentiated,  showing  now  cejls 
lying  in  a  distinct  ground-mass.  The  masses  appear  in  the  form  of 
flat  bands  lying  against  the  outer  sheath  of  the  notochord.  The 
bands  come  down  quite  close  to  the  aorta,  and  it  is  at  their  lower  end 
that  we  find  the  cartilage  best  defined.  In  the  hinder  dorsal  region 
the  bands  appear  to  descend  to  a  lower  level  on  the  sides  of  the  noto- 
chord, the  lower  ends  coming  into  quite  close  contact  with  the  aorta. 
Furthermore,  each  band,  or  arch-base,  sends  outward  from  near  its 
upper  end  a  short  process  into  the  region  where  later  the  proximal 
end  of  a  rib  will  appear.  This  may  be  seen  throughout  the  whole 
trunk  region.  In  the  tail  the  halves  of  each  lower  arch  have  united 
at  their  distal  ends,  so  as  to  enclose  the  blood  vessels. 

My  specimen  next  in  length  to  those  just  described  is  23mm. 
long.  In  this  the  notochord  has  attained  a  diameter  of  about  .4mm, 
exclusive  of  the  two  sheaths.  The  epithelial  layer  has  no  longer  the 
distinct  appearance  that  it  had  in  the  preceding  stage.  Here  and 


28  FIELD  COLUMBIAN  MUSEUM — ZOOLOGY,  VOL.   i. 

there  nuclei  may  be  distinguished  in  the  deeply  staining  layer  which 
surrounds  the  notochord ;  but  the  latter  has  in  many  places  an  appear- 
ance as  if  it  also  had  become  vacuolated.  If  so,  the  mesh  work  is  very 
fine.  I  have  not  in  any  stage  of  development  seen  any  such  columnar 
epithelium  as  that  figured  by  Hasse.  (39,  Taf.  vi.,  Fig.  14.) 

It  may  be  as  well  to  state  here  that  I  have  measured  the  diame- 
ter of  the  notochord  in  specimens  up  to  44mm.  in  length,  and  find 
that  in  the  vertebral  regions,  where  it  is  of  course  most  constricted, 
the  diameter  has  not  appreciably  increased  beyond  about  .4mm.  And 
yet  in  a  specimen  about  12.5011.  the  opening  through  the  vertebral 
•centrum  has  a  diameter  of  about  .6mm.,  and  this  is  filled  up  by  the 
.notochord,  which  retains  the  appearance  it  has  in  younger  specimens. 
This  shows  that  this  organ,  instead  of  being  suppressed  by  the  devel- 
opment of  the  cartilaginous  and  bony  structures  that  develop  around 
it,  continues  to  grow  slowly  until  the  animal  reaches  a  considerable 
size.  In  respect  of  its  notochord,  Amia  displays  a  transitional  stage 
between  the  lower  "Ganoids"  and  the  "  Teleosts." 

Surrounding  the  notochord  of  the  specimen  23mm.  in  length  is 
found  the  cuticular  sheath,  whose  thickness  has  increased  greatly 
since  the  earlier  stage.  This  thickness  is  now  about  .O2mm.  There 
.are  seen  to  be  indications  of  the  fibrous  structure,  which  has  been 
observed  by  several  writers.  Outside  of  the  just  described  cuticu- 
lar sheath  is  the  elastica.  It  forms  a  thin,  highly  refractive  lin»-  in 
cross-sections,  and  often  presents  a  wavy  course.  This  I  attribute 
to  distortion  due  to  postmortem  changes.  I  have  never  found  in  it 
the  slightest  indication  of  cells,  nuclei,  or  any  other  structure. 

The  axial  structures  outside  of  the  notochord  and  its  coverings 
are  of  great  interest.  Throughout  the  length  of  the  body  the  lateral 
halves  of  the  neural  arches  have  met  above  the  neural  canal,  and 
their  backwardly  directed  distal  ends  lie  alongside  of  each  other.  As 
is  known,  they  never  unite  to  form  neural  spines.  Interspinous  car- 
tilages are  also  now  developed,  both  above  and  below.  The  proxi- 
mal member  (axonost)  is  long  and  slender,  its  proximal  extremity 
reaching  nearly  to  the  tips  of  the  arches,  upper  and  lower.  Each 
is  followed  distally  by  two  short  nodules  of  cartilage. 

In  a  cross-section  through  the  dorsal  region,  the  upper  arches 
may  be  seen  to  rest  on  short  cartilages  which  themselves  come  in  con- 
tact by  their  lower  ends  with  the  elastica  (Fig.  9) .  Against  the  right 
.and  left  sides  of  the  notochordal  rod  we  find  the  bases  of  the  lower 
arches.  These,  as  in  the  case  of  the  upper  arches,  are  of  hyaline 
•cartilage,  and  their  bases  are  in  direct  contact  with  the  notochordal 
sheaths.  Distally  there  is  attached  to  the  outstanding  process  of  the 


OCT.  1895.  VERTEBRAL  COLUMN  OF  AMIA — HAY  29 

half-arch  on  each  side  a  bar  of  cartilage,  the  rib.  This  rib,  as  in  the 
case  of  the  ribs  of  osseous  fishes,  passes  outward  immediately  between 
the  peritoneum  and  the  lateral  muscles. 

Anteriorly,  at  the  third  vertebra,  the  bases  of  the  lower  arch 
stand  at  the  sides  of  the  notochord  close  to  the  bases  of  the  upper 
arch,  but  I  do  not  think  that  they  at  any  time  coalesce.  As  a  series 
of  sections  are.  run  through  toward  the  rear,  the  bases  of  the  lower 
arches  descend  to  a  lower  level  and  a  greater  space  intervenes  between 
them  and  the  upper  arches. 

It  has  already  been  noted  that  the  bases  of  the  lower  arches, 
especially  along  the  anterior  portion  of  the  vertebral  column,  send 
downward  towards  the  aorta  on  each  side  a  process  of  cartilage. 
As  may  be  seen  from  Fig.  9,  the  lower  end  of  this  thickens  and 
grows  downward,  so  as  to  project  a  slight  distance  below  the  noto- 
chord. These  lower  swellings  of  the  cartilage  are,  as  may  be  sur- 
mised, the  beginnings  of  the  lowest  cartilaginous  rays  which  have 
been  described  as  occurring  in  the  adult  vertebrae,  and  which  have 
been  called  the  aortal  supports.  My  supposition,  derived  from  the 
examination  of  these  structures  in  the  adult,  that  they  originate  from 
the  lower  arches  is  fully  confirmed.  As  in  the  case  of  the  lower 
arches  themselves  these  aortal  supports  develop  from  the  front  to  the 
rear.  When  a  specimen  3omm.  long  is  examined  by  means  of  cross- 
sections,  it  is  seen  that,  when  about  the  twenty-fourth  vertebra  is 
reached,  the  aortal  support  is  cut  off  from  the  main  cartilage  by  a 
narrow  spicule  of  bone.  Behind  this  region  the  support  is  apparently 
developed  independently  of  the  main  mass  of  the  lower  arch.  The 
whole  appearance  suggests  that  this  terminal  portion  of  the  arch- 
base,  becomes  developed  into  true  cartilage  just  a  little  too  late  to 
escape  being  separated  from  its  parent  mass  by  the  now  developing 
bone. 

Scheele  (55)  has  observed  in  certain  Cyprinidae  (Rhodeus)  struc- 
tures which,  consisting  of  fibrous  tissue,  arise  from  the  lower  and 
hinder  portions  of  the  lower  arches,  and  descending  on  each  side 
unite  below  the  aorta.  This  vessel  is  therefore  surrounded  below 
each  vertebral  body  by  this  structure  and  supported  and  protected 
by  it.  Scheele  regarded  it  as  an  outgrowth  from  the  base  of  the 
lower  arch,  and  I  think  that  he  was  correct  in  his  conclusion.  The 
structures  which  he  describes  are  undoubtedly  homologous  with  the 
aortal  supports  of  Amia.  But  in  the  Cyprinidae  there  has  occurred 
an  enormous  reduction  of  the  cartilage  which  usually  enters  into  the 
formation  of  the  axial  structures,  and  these  supports  have  felt  the 
effect  of  it.  I  think  that  in  most  fishes  there  will  be  found  on  the 


.30  FIELD  COLUMBIAN  MUSEUM — ZOOLOGY,  VOL.   i. 

lower  side  of  the  vertebras  some  rudiment  of  these  supports,  either 
in  the  form  of  bone  or  dense  connective  tissue. 

But  Scheele  is  not  content  merely  to  note  the  occurrence  of  these 
•connective  tissue  aortal  supports.  He  regards  them  as  being  of  great 
morphological  importance,  the  representatives  of  a  series  of  arches, 
.absent,  so  far  as  yet  known,  from  all  other  Teleosts.  They  are  called 
by  him  "  hsemapophyses, "  not  indeed  homologous  with  what  have 
usually  been  called  such  in  the  tail  of  osseous  fishes,  but  with  the 
lower  arches  in  the  tail  of  Selachians,  Urodeles  and  Ganoids.  Scheele 
would  have  us  believe  that  in  Rhodeus  there  are  present  representa- 
tives of  three  series  of  arches,  viz.:  (i)  the  neural  arches,  (2)  the 
ribs  and  their  homologues  in  the  tail  which  enclose  the  haemal  canal, 
.all  of  which  he  calls  parapophyses,  and  (3)  the  vestigial  ' '  haemapo- 
physes."  The  latter  have  been  inherited  from  the  Selachians  and 
•Ganoids,  but  have,  with  the  alleged  exception  of  those  of  Rhodeus, 
"been  lost  in  the  Teleosts.  The  parapophyses,  therefore,  belong  to  a 
.series  of  arches  which  are  placed  at  a  higher  level  in  the  body  of  the 
iish,  derived  originally,  indeed,  Scheele  claims,  from  the  upper  arches, 
"  Theile  der  obern  Bogen." 

Now,  there  is  not  an  argument  advanced  by  Scheele  for  the  pur- 
pose of  establishing  his  ideas  regarding  the  aortal  supports  as  repre- 
sentatives of  a  hitherto  unrecognized  series  of  arches  in  Teleost 
fishes,  and  as  homologous  with  the  lower  arches  of  sharks,  and  Gan- 
oids, and  Urodeles,  that  will  not  apply  with  greater  force  to  the  car- 
tilages which  support  the  aorta  in  Amia.  And  yet  it  is  perfectly  ob- 
vious that  these  processes  from  the  parapophyses  do  not  become  mod- 
ified in  this  Ganoid's  tail  into  the  lower  arches.  As  we  pass  back- 
ward in  a  series  of  cross-sections  of  an  Amia  27mm.  long,  we  find 
that  near  the  last  dorsal  vertebra,  the  cartilaginous  bases  of  the  lower 
.arches  assume  in  section  a  triangular  form.  The  parapophyses  arise 
from  the  upper  outward  angle,  the  one  pointing  outward  beneath 
the  peritoneum,  the  aorta  supports  from  the  lower  inner  angle.  The 
outer  angle  is  plainly  prolonged  in  the  last  dorsal  vertebra  ;  \vhile  in 
the  next  vertebra,  the  first  caudal,  it  is  united  with  its  fellow  beneath 
the  caudal  vessels.  In  short,  the  parapophyses  are  developed  from 
the  upper  portion  of  the  bases  of  the  lower  arches,  the  aortal  sup- 
ports from  the  lower  portion.  The  latter  are  simply  differentiated 
parts  of  the  bases  of  the  lower  arches. 

In  Fig.  i  o  is  shown  a  sagittal  section  through  the  axial  region  of 
a  specimen  of  Amia  somewhat  larger  than  the  one  just  studied;  it  is 
3omm.  long.  The  section  includes  the  anterior  and  a  portion  of  the 
middle  tail  region.  The  notochord  and  its  two  sheaths  are  repre- 


OCT.  1895.  VERTEBRAL  COLUMN  OF  AMIA — HAY  31 

sented,  and  the  cartilages  that  rest  on  them  above  and  below.  Wher- 
ever these  cartilages  come  in  contact  with  the  notochord,  the  latter 
structure  is  seen  to  be  slightly  constricted,  more  in  the  case  of  the 
larger  cartilages  than  of  the  smaller  ones. 

But  the  cartilaginous  structures  are  of  the  greatest  interest  to  us. 
We  are  now  in  the  region  in  which,  in  the  adult,  there  occurs  a  change 
from  the  single  to  the  double  vertebrae.  The  arches  which  are  seen 
on  the  extreme  left  of  the  figure  are  those  of  the  second  caudal  ver- 
tebra Between  the  long  haemapophyses  toward  the  right  are  seen 
three  small  nodules  of  cartilage.  On  the  upper  side  of  the  notochord 
are  seen  other  neural  arches,  and  between  the  bases  of  those  on  the 
right  hand  two  small  cartilages  like  those  found  between  the  lower 
arches.  But  it  is  evident  from  the  section  that  a  third  little  mass  of 
cartilage  has  fused  with  the  base  of  the  next  half-arch  toward  the 
right.  The  section  being  taken  a  little  to  one  side  of  the  middle  line, 
it  is  evident  that  for  each  little  nodule  of  cartilage  seen,  there  is  an- 
other on  the  opposite  side.  Hence  there  would  be  four  such  masses 
in  front  of  the  upper  and  lower  arches  belonging  to  each  myomere. 

It  will  be  further  observed  that  the  upper  arches  on  the  left  side 
of  the  figure  appear  to  be  segmented  at  short  distance  below  their 
bases,  while  the  upper  arches  standing  behind  the  small  nodules  of 
cartilage  are  not  thus  segmented.  This  suggests  that  those  basal 
pieces  on  which  the  larger  portion  of  each  half-arch  appears  to  rest 
are  really  the  equivalents  of  those  little  masses  which  lie  between  the 
undivided  arches.  This  is  shown,  too,  I  think,  not  only  from  the 
fact  that  the  little  cartilages  of  the  middle  tail  region  and  the  basal 
pieces  of  the  region  in  front  of  them  occupy  corresponding  positions, 
but  also  because  of  the  similarity  in  the  manner  of  their  development. 
Both  are  evidently  formed  in  the  intervals  between  the  bases  of  the 
arches  immediately  in  front  and  behind.  Those  of  the  dorsal  and  an- 
terior tail  region  secondarily  push  themselves  backward  under  the 
bases  of  the  neural  arches.  The  upper  arches  become  differentiated 
first,  and  their  bases  come  down  to  the  membrana  elastica.  At  the 
same  time  incipient  cartilage  cells  may  be  made  out  lying  between 
the  bases,  possibly  continuous  with  them.  Later,  these  also  are  trans- 
formed into  clear  cartilage,  and  increasing  in  size  so  as  almost  to 
touch  one  another,  they  push  the  bases  of  the  neural  arches  away 
from  contact  with  the  notochord. 

In  the  case  of  the  lower  arches  of  the  dorsal  region,  we  do  not 
find  little  cartilages  lying  between  them.  On  the  contrary,  we  find 
that  the  anterior  end  of  the  base  of  each  half-arch  has  grown  forward, 
vso  as  to  occupy  the  place  of  the  missing  nodule.  Or,  it  is  posssible 


32  FIELD  COLUMBIAN  MUSEUM — ZOOLOGY,  VOL.   i. 

that  at  sometime  in  the  history  of  the  larva,  or  during  its  ancestral 
history,  the  base  of  the  lower  half-arch  has  fused  with  the  little  inter- 
mediate cartilage  which  lay  in  front  of  it ;  but  I  have  seen  no  signs 
of  its  presence.  It  has  likely  been  suppressed.  Now,  as  will  be 
readily  conjectured,  and  as  will  be  further  demonstrted,  the  ''interca- 
lated vertebrae"  of  the  adult,  or  as  we  have  called  tjiem,  tJie  pleurocentra, 
have  originated  from  the  four  little  masses  of  cartilage  lying  in  front  of 
the  arches  belonging  to  each  myomere;  while  the  hypocentra  have  had  their 
origin  from  the  union  of  the  upper  and  lower  arches.  Furthermore,  the 
simple  vertebra  of  the  region  in  front  of  this  are  developed  from  the  bases 
of  the  lower  arches  and  the  basal  cartilages  on  which  the  upper  arches 
rest. 

Again,  there  are  none  of  the  extra  cartilages  placed  between  the 
bases  of  the  upper  and  lower  arches  in  the  upturned  region  of  the 
tail.  It  is  possible  that,  on  account  of  the  crowding  together  of 
structures  in  this  region,  these  nodules  never  made  their  appearance 
there.  Or,  being  possibly  younger  productions,  they  were  the  first  to 
feel  the  effects  of  influences  leading  to  degeneration,  and  at  length 
disappeared. 

Before  we  investigate  the  later  history  of  the  arches  and  the 
accompanying  cartilages,  it  will  be  well  to  inquire  whether  anything 
corresponding  to  the  latter  occur  elsewhere,  especially  in  related 
lower  forms.  These  are  found  in  a  position  entirety  similar  to  what 
are  called  intercalated  cartilages  in  sharks.  Whether  or  not  they  are 
homologous  structures  in  the  two  forms  I  do  not  here  decide.  But 
similar  intercalated  cartilages  are  found  also  in  the  cartilaginous  Gan- 
oids. Fig.  it  has  been  drawn  from  the  dorsal  region  of  Acipen- 
3er.  Here  we  have  upper  and  lower  arches  resting  by  their  bases- 
on  the  sheath  of  the  large  and  partly  exposed  notochord.  Between 
the  bases  of  the  upper  arches  are  seen  intercalated  masses  of  cartilage, 
each  mass  consisting  of  from  one  to  four  pieces.  Between  the  ex- 
panded bases  of  each  two  of  the  lower  arches  is  also  a  group  of  car- 
tilages varying  in  number,  size  and  form.  These  cartilages  were 
long  ago  observed  by  V.  Baer  and  J.  Muller.  (V.  Baer,  2;  J.  Muller, 
49,  p.  87.)  While  these  intercalated  cartilages  are  thus  broken  up  in 
Acipenser  into  a  number  of  distinct  pieces,  we  find  that  in  Polyodon 
(Spatularia)  each,  "both  above  and  below,  consists  of  a  single  piece. 
See  figure  of  a  portion  of  the  vertebral  column  of  Spatularia  in 
Wiedersheim's  "  Vergleichende  Anatomic  der  Wirbelthiere." 

If  now,  in  either  Acipenser  or  Polyodon,  the  upper  intercalated 
masses  were  to  increase  in  size  to  any  considerable  extent  in  an  ante- 
rio-posterior  direction,  the  bases  of  the  upper  cartilages  would  be 


OCT.  1895.  VERTEBRAL  COLUMN  OF  AMIA — HAY  33. 

either  lifted  tip  out  of  contact  with  the  notochord  or  be  suppressed.  If 
in  addition  to  this,  the  lower  intercalated  cartilages  were  to  be  sup- 
pressed or  to  become  fused  with  the  bases  of  the  lower  arches,  we 
should  have  exactly  the  same  condition  that  we  find  in  the  greater 
part  of  the  vertebral  axis  of  the  young  Amia. 

'  It  has  already  been  shown  that  in  Amia  the  notochord  is  not  at 
any  stage  surrounded  by  a  tube  of  cartilage.  At  most  there  are  to 
be  found  only  four  bands  of  more  or  less  differentiated  cartilage,  two 
above  and  two  below  the  notochord,  and  it  is  not  certain  that  these 
bands  are  continuous.  In  Lcpisosteus,  however,  according  to  Balfour 
and  Parker  (4)  the  notochord  is  at  one  stage  almost  completely  en- 
closed by  a  tube  of  well  defined  cartilage.  The  tube  is  interrupted 
only  by  gaps  at  the  sides  of  the  notochord  between  the  bases  of  the 
upper  and  the  lower  arches.  Nothing  like  distinct  and  independent 
intercalated  cartilages  were  observed" by  these  authors;  but  "inter- 
vertebral  rings  of  cartilage "  were  observed  and  figured  by  them. 
These  were  placed  in  the  intervals  between  successive  pairs  of  arches, 
and  completely  surround  the  section  of  the  notochord  where  they 
occur.  Balfour  and  Parker  found  that  these  rings  do  not  have  a  uni- 
form thickness,  but  that  each  showed  two  dorsal  and  two  ventral 
thickenings.  These  thickenings  are  in  line  with  the  bases  of  the 
arches,  and  were  regarded  by  the  observers  as  presumptive  evidence 
that  the  rings  had  been  produced  through  the  fusion  of  the  bases. 
However,  there  were  missing  the  very  stages  in  which  the  rings  took 
their  origin,  and  it  is  by  no  means  certain  that  they  are  not  produced 
from  the  fusion  of  four  intercalated  cartilages  for  each  body  segment. 
If  the  four  intercalated  cartilages  of  each  segment  in  the  tail  of  Amia 
should  expand  and  then  fuse  with  one  another  and  with  the  adjacent 
bases  of  arches,  we  should  have  the  condition  found  in  Lepisosteus. 

Ossification  of  the  vertebral  column  begins  probably  soon  after 
the  young  Amia  has  reached  a  length  of  i5mm.  At  least,  no  deposit 
of  bony  matter  has  been  observed  in  specimens  of  this  length,  while 
such  deposits  are  abundant  in  a  specimen  23mm.  long. 

The  place  of  origin  of  the  earliest  formed  bone  of  the  vertebra? 
of  fishes  has  been  much  discussed  and  has  received  from  investiga- 
tors the  most  varied  and  often  contradictory  answers.  In  the  settle- 
ment of  this  question  is  further  involved  the  view  that  is  to  be  held 
concerning  the  composition  of  the  vertebra,  especially  whether  or 
not  any  part  of  it  is  derived  from  the  envelops  of  the  notochord.  In 
discussing  this  subject  we  shall,  for  the  sake  of  brevity,  consider  that 
any  part  of  the  notochord  or  of  its  sheaths  which  does  not  change  to 
either  cartilage  or  bone  does  not  form  a  portion  of  the  vertebra. 


34  FIELD  COLUMBIAN  MUSEUM — ZOOLOGY,  VOL.   i. 

Von  Baer  (2  p.  36), basing  his  conclusions  on  his  studies  especially 
of  the  Cyprinidae,  thought  that  no  part  of  the  vertebra  is  derived  from 
the  notochord  or  its  sheaths.  For  him  the  vertebra  was  formed 
through  the  simple  union  of  the  bone  arising  from  the  upper  and  the 
lower  arches  and  extending  around  the  notochord  so  as  to  produce 
a  ring. 

From  the  study  of  Blennius  viviparus  Rathke  (51)  concluded  that 
each  vertebral  centrum  arises  from  ossifications  which  are  located  in 
the  bases  of  the  upper  and  the  lower  arches,  which  four  points  by 
their  union  form  a  ring.  Later  Rathke  (52)  appears  to  have  accepted 
J.  M tiller's  view  that  the  vertebral  ring  is  distinct  in  its  origin  from 
the  arches. 

Johann  Miiller  at  first  (49,  Osteology,  pp.  83  and  143)  held  the 
opinion  that  ossification  of  the  vertebral  column  begins  outside  of  the 
notochordal  sheaths,  and  that  the  vertebra  is  composed  wholly  of  the 
arches  and  the  ossifications  arising  in  them.  Later,  from  studies  on 
the  Elasmobranchs,  he  concluded  (49,  Neurology,  p.  69)  that  in  the 
case  even  of  the  osseous  fishes,  the  notochordal  sheath  ossifies,  and 
that  an  undivided  ring  is  formed  independently  of  the  arches.  The 
vertebra  then  consists  of  the  upper  and  the  lower  arches  and  the  cen- 
tral ring. 

August  Miiller's  views  are  essentially  those  of  Johann  Miiller  (48, 
p.  260.) 

Gegenbaur  has  expressed  his  conclusions  on  the  origin  of  the  ver- 
tebral body  in  his  paper  on  Lepisosteus  (28.)  He  believes  that  the 
centrum  arises  outside  of  the  elastica  externa,  and  that  it  proceeds 
from  the  arches  themselves. 

Theophil  Lotz  (45)  made  investigations  on  Salmo  salar.  For  him 
the  vertebral  centrum  arises  outside  of  the  elastica,  its  earliest  ap- 
pearance being  at  the  points  of  contact  of  the  lower  arches  with  the 
notochordal  sheaths.  It  then  grows  upward  on  each  side  of  the  no- 
tochord, and  its  extremities  at  length  pass  under  the  bases  of  the 
upper  arches  and  meet  above  the  notochord  to  form  a  complete  ring. 

Oscar  Cartier  (13)  agrees  with  Lotz,  except  that  he  finds  that  the 
ossification  which  produces  the  ring  arises  in  the  elastica.  The  latter 
disappears  as  the  ring  is  developed. 

Goette  (32  and  33)  contends  that  ossification  begins  in  what  is 
usually  called  the  elastic  sheath.  He  denies  the  elastic  nature  of 
this  sheath,  and  holds  that  it  is  cellular  in  structure.  The  centrum 
is  developed  from  below  upward,  as  taught  by  Lotz  and  Cartier. 

Balfour,  in  1881,  in  his  Comparative  Embryology  appears  to 
accept  in  general  the  views  of  Goette. 


OCT.  1895.  VERTEBRAL  COLUMN  OF  AMIA — HAY  35 

In  1882  Balfour  and  Parker  published  their  extremely  important 
paper  on  the  structure  and  development  of  Lepisosteus  (4).  They 
showed  in  this  work  that  there  is  surrounding  the  notochorda  cuticular 
sheath  and  a  very  distinct  elastica  externa.  Cartilaginous  arches 
arise  both  above  and  below  the  notochord,  their  bases  coming  into 
•contact  with  the  elastica.  At  a  somewhat  later  stage,  there  is  found 
to  be  an  almost  complete  tube  of  cartilage  surrounding  the  notochord 
outside  of  the  elastica.  This  has  already  been  described  on  another 
page.  At  this  stage  a  thin  crust  of  bone  envelops  the  upper  and  the 
lower  arches  and  the  whole  vertebral  body.  But  the  bone  has  not 
arisen  in  the  elastic  layer  of  the  notochord,  neither  does  it  extend  into 
this.  While  its  exact  place  and  manner  of  origin  is  so  far  unknown, 
it  apparently  does  not  even  arise  close  to  the  elastic  sheath,  but  is 
separated  from  the  latter  by  the  layer  of  cartilage.  Here,  so  far 
as  we  can  see  and  as  was  believed  by  Balfour  and  Parker,  the  verte 
brae  originate  from  the  union  simply  of  the  two  sets  of  arches  and 
their  subsequent  ossification. 

Klaatsch  (41  and  42)  holds  that  the  vertebrae  of  the  Teleostomi 
arise  wholly  outside  of  the  notochordal  sheath. 

Scheele  (55)  who  has  investigated  Rhodeus  among  the  Cyprinidae 
and  the  Trout  among  the  Salmonidae,  regards  the  skeletogenous  layer 
outside  of  the  elastica  as  giving  origin  to  all  the  ossified  portions  of 
the  vertebrae. 

As  a  result  of  my  investigations  I  conclude  that  in  Arnia,  ossifi- 
cation of  the  vertebral  centrum  does  not  begin  in  either  the  cuticular 
sheath  or  in  the  elastica.  On  the  contrary,  it  takes  its  origin  wholly 
in  the  layer  of  embryonic  connective  tissue  which  lies  immediately 
outside  of  the  elastica.  The  latter  notochordal  sheath  may  be  seen 
in  young,  just  ossifying  Amia,  and  even  in  adults  with  a  length  of 
i2.5cm.,  as  a  bright,  highly  refractive  line  immediately  between  the 
layer  of  developing  bone  and  the  cuticular  sheath.  Indeed  it  is  n'ot 
infrequent  that  one  may  distinguish  cells  resembling  bone-cells  lying 
between  the  elastica  and  the  lamella  of  growing  bone.  This  is  most 
likely  to  be  observed  near  the  ends  of  the  centra. 

The  earliest  osseous  rudiments  of  the  vertebral  body  do  not  form  an 
undivided  ring.  On  the  contrary,  the  bone  which  is  to  lay  the  foun- 
dation of  each  centrum  starts  from  a  number  of  distinct  points. 
These  are  located  in  the  angles  between  the  right  and  left  sides  of 
each  half -arch  and  the  adjacent  portion  of  the  membrana  elastica. 
There  are  thus  two  of  these  centers  of  ossification  for  each  half-arch 
.and  two  for  each  of  the  intercalated  cartilages  of  the  middle  tail 
region  (Fig.  12).  I  have  thoroughly  satisfied  myself  by  the  exam- 


2,6  FIELD  COLUMBIAN  MUSEUM — ZOOLOGY,  VOL.   i. 

ination  of  cross  and  longitudinal  sections  that  the  bony  deposits  found 
at  the  base  of  each  half  arch  do  not  at  first  extend  all  around  the 
base.  The  bone  is  wanting  both  in  front  and  behind  the  base; neither 
does  it  pass  between  the  base  and  the  elastica. 

While  it  is  possible  to  regard  these  centers  of  bone  growth  as 
'common  to  the  arches  an,d  to  the  tissues  in  which  the  primitive  ring 
is  developed,  as  Rathke  thought,  they  appear  to  appertain  more 
properly  to  the  arches.  On  their  first  appearance  they  extend  fur- 
ther up  on  the  arch  than  they  do  along  the  circumference  of  the  no- 
tochord,  and  in  many  instances  they  are  seen  hardly  to  touch  the  lat- 
ter. In  other  words,  the  centers  belong  to  the  arches  rather  than  to 
any  tissue  in  closer  relations  with  the  notochord.  However,  the  little 
deposits  of  bone  soon-  begin  to  extend  themselves  over  the  notochord 
more  rapidly  than  along  the  arches,  and  then  they  appear  to  belong 
rather  to  the  former. 

The  bone  is  perichondrial  in  its  origin  where  it  is  in  connection 
with  the  cartilage  of  the  arches.  It  forms  at  first  an  extremely  thin 
layer  wholly  devoid  of  any  bone-cells,  but  as  the  layer  thickens  these 
cells  are  seen  to  be  included.  When,  however,  the  bone  lies  against 
the  membrana  elastica,  the  bone  cells  are  included  from  the  start. 

Through  the  extension  of  the  various  centers  of  each  vertebra 
around  the  notochord  and  their  union  with  one  another,  a  continuous 
ring  of  bone  is  formed.  Meanwhile,  the  two  centers  at  the  base  of 
each  arch  have  grown  forward  and  backward  and  met,  and  the  deposit 
continues  to  advance  until  it  covers  the  whole  centrum  with  a  bony 
crust.  In  a  larva  3omm.  long,  ossification  has  so  far  advanced  in  the 
dorsal  region  as  to  join  all  the  centers  into  one  band,  which  has 
attained  nearly  the  full  length  of  the  centrum ;  while  in  the  middle 
of  the  tail  only  a  tiny  flake  of  bone  is  to  be  seen  on  each  side  of  the 
base  of  each  half-arch. 

Soon  after  the  vertebral  band  has  closed  around  the  notochord 
the  bone  begins  to  push  itself  out  into  the  connective  tissue.  The 
new  deposit  is  in  the  form  of  narrow  bars  which  shoot  out  at  right 
angles  from  the  primitive  ring,  and  these  again  become  united  by 
other  bars  more  or  less  parallel  with  the  ring.  A  loose  meshwork 
of  bone  is  thus  finally  produced,  such  as  is  to  be  seen  in  the  adult 
vertebra.  This  network  of  bony  spicules  is  first  seen  between  the 
bases  of  the  lower  arches  of  the  dorsal  region  in  the  loose  connective 
tissue  just  above  the  aorta. 

In  the  case  of  the  centers  of  ossification  belonging  to  the  bases 
of  the  lower  arches  in  the  trunk  region,  I  find  the  bone  appearing  on 
the  lower  surface  of  the  cartilage,  both  mesiad  and  laterad  of  the 


OCT.  1895.  VERTEBRAL  COLUMN  OF  AMIA — HAY  37 

aortal  support  (Fig.  12).  The  latter  structure  is,  of  course,  even 
in  adult  life,  not  covered  with  bone  at  its  distal  end.  Whether  the 
bone  found  on  the  two  sides  of  this  originates  on  one  side  and  then  ex- 
tends around  it  to  the  other,  or  whether  there  are  two  distinct  centers, 
I  am  unable  now  to  say.  As  already  remarked,  it  is  found  that  along 
the  posterior  dorsal  region  the  crust  of  bone  is  developed  a  little 
sooner  than  the  cartilaginous  aortal  support,  so  that  the  latter  never 
lias  a  direct  connection  with  the  main  portion  of  the  cartilage  of  the 
lower  arch.  The  hindermost  of  the  supports  are  rather  tardy  in 
making  their  appearance.  As  already  stated,  all  the  intercalated  car- 
tilages, both  of  the  dorsal  and  of  the  caudal  regions,  become  ossified, 
«ach  from  the  two  centers,  which  soon  unite  into  one.  The  upper 
half-arches  of  the  dorsal  and  anterior  tail  regions  are  incrusted  each 
with  a  sheath  of  bone,  which  arises  at  an  earlier  period  than  do  the 
ossifications  closer  to  the  notochord.  This  sheath  covers  each  half- 
arch  except  at  the  proximal  and  distal  ends.  The  upper  half-arches 
of  the  middle  tail  region  and  all  of  the  lower  half-arches  have  ossifica- 
tions at  their  bases,  next  to  the  notochord,  each  arising  from  two  cen- 
ters, and  have  also  a  sheath  of  bone  covering  the  greater  extent  of 
their  length.  This  sheath,  as  in  the  case  of  the  dorsal  half-arches, 
leaves  the  distal  extremity  of  the  cartilage  free,  and  proximally  comes 
down  close  to  the  basal  ossification,  without,  however,  ever  uniting 
with  it  at  any  time  of  life.  We  may  therefore  say  that  each  half- 
arch  has  two  ossifications,  that  contiguous  to  the  notochord  and  the 
distal  sheath,  except  the  upper  half-arches  of  the  dorsal  and  anterior 
tail  regions.  These  have  only  the  distal  sheath,  and  lack  the  basal 
ossification.  My  judgment  is  that  the  latter  has  been  suppressed  by 
the  ossification  arising  from  the  neighboring  intercalated  cartilage. 
The  cartilage  found  in  each  half-aich  is  unbroken  from  the  notochord 
to  the  tip,  except  those  of  the  dorsal  and  anterior  tail  regions. 

We  are  now  to  learn  how  the  vertebral  bodies  of  the  different 
regions  are  formed.  In  the  trunk  and  anterior  tail  regions  each  cen- 
trum is  produced  by  the  fusion  of  the  bones  which  have  arisen  from  the 
upper  intercalated  cartilages  with  those  at  the  bases  of  the  correspond- 
ing lower  arches.  The  upper  arch  has  nothing  whatever  to  do  with  the 
formation  of  the  centrum.  Its  sheath  simply  rests  on  the  upper  sur- 
face of  the  centrum,  and  is  separated  from  it  by  a  permanent  suture. 
A  parapophysis  of  less  or  greater  length  forms  on  each  side,  a  part 
of  each  vertebral  centrum,  being  originally  a  portion  of  the  lower 
arch.  In  the  anterior  tail  region  there  is  no  parapophysis,  the  ossifi- 
cation not  extending  beyond  the  surface  of  the  vertebra. 


38  FIELD  COLUMBIAN  MUSEUM — ZOOLOGY,  VOL.   i. 

In  the  middle  tail  region  we  find  apparently  two  kinds  of  centrar 
those  with  and  those  without  arches.  The  latter,  the  so-called  pleu- 
rocentra,  are  formed  wholly  through  the  union  of  the  ossifications 
arising  from  the  upper  with  those  arising  from  the  lower  intercalated 
cartilages.  Of  course  the  cartilages  themselves  continue  to  consti- 
tute a  part  of  such  a  centrum.  On  the  other  hand,  the  centra  of  this 
region  which  are  furnished  with  upper  and  lower  arches  are  produced 
through  the  fusion  of  the  ossifications  which  arise  at  the  bases  of 
these  two  arches.  They  contain  nothing  more ;  unless,  to  be  exact,, 
we  expressly  mention  the  persisting  cartilage  and  the  enclosed  por- 
tion of  the  notochord  and  its  sheaths. 

The  posterior  tail  vertebrae  are  mostly  like  the  vertebrae  last  de- 
scribed. They  are  produced  wholly  through  the  union  of  the  bases 
of  the  upper  and  lower  arches.  We  find,  therefore,  in  the  vertebral 
column  of  Amia  no  support  for  the  doctrine  that  the  vertebra  is  com- 
posed partly  of  a  central  portion  which  is  distinct  in  origin  from  the 
cortical  portions,  and  which  has  its  origin  in  one  of  the  notochordal 
sheaths.  In  Amia  the  whole  vertebra  originates  from  the  ossifications- 
which  spread  out  from  the  bases  of  the  arches  or  from  the  intercal- 
ated cartilages,  or  from  both.  Clear  evidences  to  the  same  effect  are 
given  by  Balfour  and  Parker's  work  on  Lepisosteus.  In  that  fish,  too, 
neither  of  the  notochordal  coverings  furnished  any  portion  of  the 
vertebral  centrum ;  all  the  bone  developed  from  the  cartilages  sur- 
rounding the  notochord.  Indeed,  it  is  only  where  there  are  gaps  in 
the  cartilaginous  tube  surrounding  the  notochord  that  the  bone  comes 
at  all  in  contact  with  the  elastica,  and  evidently  the  bone  did  not  orig- 
inate where  these  gaps  are.  The  notochord  can  therefore  hardly  be 
truly  said  to  take  the  active  part  in  the  development  of  the  bony  ver- 
tebral axis  that  some  authorities  have  attributed  to  it. 

Nevertheless,  I  am  not  prepared  to  say  that  the  coverings  of  the 
notochord  never  undergo  ossification.  In  some  of  the  more  advanced 
larvae  of  Amia  itself,  I  find  that  the  inner  sheath,  the  cuticula  chordae, 
has  every  optical  appearance  of  having  become  calcified,  and  it  stains- 
exactly  like  the  basis  of  the  bone  outside  of  the  sheaths.  But  I  am 
not  sure  that  this  has  happened.  Goette  agrees  with  Kolliker  that  in 
Anguilla  the  cuticula  chordae  undergoes  partial  ossification  (33,  p. 
125).  It  is,  however,  the  outer  sheath,  the  elastica,  which  is  regarded 
by  some  writers  as  calcifying  and  furnishing  the  primitive  ring  of  the 
vertebra.  It  is  quite  certain  that  this  elastica  is  a  secretion  product 
of  the  innermost  layer  of  the  skeletogenous  tissue.  It  would  not 
then  be  strange  if  the  earliest  film  of  bony  substance  poured  out  by 
this  skeletogenous  tissue  were  to  occupy  the  apposed  elastica.  But 


OCT.  1895.  VERTEBRAL  COLUMN  OF  AMIA — HAY  39 

the  more  recent  investigations  are  rather  opposed  to  the  doctrine  that 
the  elastica  does  become  calcined.  It  is  quite  evident  that  primitively 
it  does  not. 

6.       FURTHER    CONSIDERATION    OF    THE    VERTEBRAL    COLUMN      OF      FOSSIL 

FISHES. 

It  becomes  now  proper  to  consider  the  composition  of  the  verte- 
brae of  the  larval  Amia  in  connection  with  the  fossil  members  of  the 
group  and  those  of  the  stegocephalous  Amphibians. 

In  doing  so  we  cannot  fail,  it  seems  to  me,  to  recognize  in  the 
upper  intercalated  cartilages  and  the  ossifications  arising  from  them, 
the  pleurocentra,  the  bones  which  cover  in  the  upper  surface  of  the 
notochord  in  both  the  ancient  Amioid  fishes  and  the  Stegocephali.  In 
a  form  like  Caturus  (Zittel,  60,  p.  138,  Fig.  146)  we  find  the  pleuro- 
centrum  occupying  a  position  between  the  bases  of  the  upper  arches 
just  as  do  the  intercalated  cartilages  in  the  tail  of  Amia.  In  Gallop- 
terus  the  upper  arches  repose  on  the  pleurocentra,  out  of  contact  with 
the  hypocentrum,  as  they  do  in  the  dorsal  region  of  Amia.  If  this  con- 
clusion is  correct,  and  the  homologising  of  the  intercalated  cartilages 
with  those  of  Acipenser  and  Poly o don  is  justified,  we  reach  the  impor- 
tant result  that  the  pleurocentrum,  which  plays  such  an  important 
part  in  some  fishes,  amphibians,  and  all  Amniota,  has  developed  from 
the  upper  intercalated  cartilages  of  the  lower  fishes. 

In  the  tail  of  our  young  Amia  these  pleurocentra  furnish  only 
the  upper  half  of  the  bony  material  which  enters  into  those  vertebral 
centra  which  have  no  arches.  The  explanation  which  has  hitherto 
been  given  of  these  centra  is,  that  the  lateral  extremities  of  the  pleu- 
rocentra have  continued  to  grow  downward  around  the  notochord 
until  they  have  met  and  coalesced  on  its  under  side.  From  Amia  we 
learn  that  this  is  not,  at  least  always,  the  case.  Two  other  elements 
in  each  muscle-segment  contribute  to  the  formation  of  this  vertebral 
ring;  these  are  the  two  lower  intercalated  cartilages  and  their  ossifi- 
cations. In  fishes  no  distinct  bones  which  correspond  to  those  lower 
elements  appear  yet  to  have  been  discovered ;  but  in  the  stegocepha- 
lous genus  Arehegosaurus,  Hermann  von  Meyer  (47,  p.  104)  has  de- 
scribed as  being  found  in  each  vertebra  a  distinct  ossification  which 
occupies  the  space  between  the  bases  of  adjacent  lower  arches,  and 
on  the  lower  side  of  the  notochord.  This  ossification  Fritsch  (Fauna 
der  Gaskohle)  calls  the  hypocentrum  pleurale.  In  the  tail  of  Archc- 
gosaurus,  according  to  Hermann  von  Meyer,  this  bone  is  divided  into 
two  lateral  halves.  In  this  condition  it  corresponds  in  every  respect 
to  the  two  ossifications  in  each  segment,  which  result,  in  an  early 


40  FIELD  COLUMBIAN  MUSEUM — ZOOLOGY,  VOL.   i. 

stage,  from  the  two  lower  intercalated  cartilages  of  Amia.  It  seems 
to  me,  therefore,  that  we  must  recognize  these  two  lower  intercalated 
cartilages  and  their  ossifications  as  representing  the  hypocentrum  pleu- 
rale.  For  the  sake  of  brevity  I  propose  in  this  paper  to  employ  for  this 
bone  the  name  hcemacentrum,  although  the  term  is  not  wholly  satisfac- 
tory. The  vertebra  which  has  hitherto  been  called  the  pleurocen- 
trum,  is  therefore  a  pleuro-haemacentrum. 

In  the  Aimioid  fishes,  and  in  the  stegocephalous  Amphibians,  as 
has  been  described,  the  lower  surface  of  the  notochord  is  often  em- 
braced, in  each  segment,  by  a  curved  plate  of  bone  which  rises  on 
the  sides  of  the  notochord  and  to  which  the  lower  arch  is  closely 
attached.  This  plate,  sometimes  divided  into  two  lateral  halves,  has 
received  the  name  hypocentrum.  In  Amia,  the  ossifications  which 
produce  the  lower  portion  of  each  centrum  that  is  provided  with 
upper  and  lower  arches,  spread  from  the  bases  of  the  lower  half-arches 
of  that  vertebra.  These  ossifications  belong  to  the  arches  from  which 
they  spring  as  truly  as  the  ossifications  connected  with  the  interca- 
lated cartilages  belong  to  the  latter.  As  already  stated  they  meet  in 
the  middle  line  below  and  grow  upward  on  the  sides  of  the  notochord. 
These  horse-shoe-shaped  pieces  of  bone  must  therefore  correspond 
to  the  hypocentra  of  the  ancient  representatives  of  Amia,  and  doubt- 
less to  the  hypocentra  of  the  Stegocephali.  I  would  therefore  define 
the  hypocentrum  as  the  vertebral  element  which  results  from  the 
union  of  the  ossifications  arising  from  the  bases  of  the  lower  arches. 
To  the  hypocentrum  may  be  attached  by  suture  or  coossification  the 
bones  springing  from  the  remainder  of  the  lower  arch.  In  the  trunk 
region  of  Amia  the  parapophyses  must  be  regarded  as  portions  of  the 
hypocentrum ;  In  the  tail  region,  the  lower  arches,  which  enclose  the 
blood-vessels,  are  morphologically  distinct  bones,  although  they  be- 
long to  the  same  cartilaginous  arches  as  the  hypocentra. 

In  Amia  the  hypocentra  of  the  middle  tail  region  grows  upward 
on  the  sides  of  the  notochord  and  unite  with  the  ossifications  which 
grow  downward  from  the  corresponding  upper  arches.  The  verte- 
•bral  centra  thus  formed  are  those  which  have  borne  the  name  of 
hypocentra,  or  intercentra.  They  are  not  hypocentra  simply.  We 
might  call  the  bone  resulting  from  the  union  of  the  ossifications  of 
the  bases  of  the  upper  arches,  epicentra.  The  vertebrae  now  under 
discussion  would  then  be  epi-hypo-centra. 

In  the  dorsal  and  anterior  tail  regions  the  vertebrae  are  produced 
each  by  the  union  of  the  hypocentrum  and  the  pleurocentrum.  They 
are  therefore  pleuro-hypocentra. 


OCT.  1895.  VERTEBRAL  COLUMN  OF  AMIA — HAY  41 

A  proper  consideration  of  the  facts  deduced  from  the  study  of 
the  development  and  composition  of  the  vertebrae  of  Amia  suffice  to 
give  us  notions  regarding  the  manner  in  which  the  vertebrae  of  this 
tish  and  its  ancestors  have  been  produced  quite  different  from  those 
which  have  hitherto  been  held.  The  two  bony  rings  belonging  to  each 
muscle-segment  of  the  tail  of  Amia,  and  of  some  other  fossil  fishes,  in- 
stead of  being  in  one  of  the  last  stages  of  vertebra-formation,  needing 
only  to  unite  in  order  to  form  a  definitive  vertebra,  are  really  in  one 
of  the  earlier  stages.  The  transformation  of  the  condition  found  in 
the  tail  of  Amia  to  that  in  the  dorsal  region,  has  apparently  been 
•effected  by  the  great  increase  in  size  of  the  hypocentral  portion  of  the 
epi-hypocentrum,  the  resulting  suppression  of  the  haemacentral  por- 
tion ot  the  pleuro-haemacentrum,  the  enlargement  of  the  pleurocen- 
tral  portion  .of  the  pleuro-haemacentrum  and  the  concomitant  sup- 
pression of  the  epicentral  portion  of  the  epi-hypocentrum.  In 
•other  words,  the  lower  portion  of  the  anterior  of  the  two  rings  was 
suppressed  by  the  expansion  of  the  lower  portion  of  the  hinder  ring, 
while  the  uppermost  portion  of  the  anterior  ring  grew  at  the  expense 
of  the  uppermost  portion  of  the  hinder  ring.  The  dorsal  vertebrae 
of  Eurycormus,  (Zittel,  60,  p.  230,  Fig.  242)  it  seems  to  me,  are  in  a 
stage  of  transition  from  the  one  condition  to  the  other.  That  the 
epicentrum,  the  ossification  at  the  bases  of  the  upper  arch,  was  at 
length  suppressed,  is  evident  from  its  not  appearing  in  either  fossil 
or  in  larval  Amias.  In  the  latter  the  upper  arch  is  not  simply  lifted 
up  out  of  contact  with  the  notochord ;  its  base  is  aborted,  the  ossifi- 
cations which  ought  to  appear  there  never  developing. 

In  case  this  course  of  transformation  has  been  pursued,  there 
must  have  been  stages  in  which  the  sutures  between  the  two  elements 
were  oblique  or  parallel  with  the  axis  of  the  fish,  instead  of  perpen- 
dicular. And  such,  indeed,  appears  to  have  been  the  condition  in 
some  of  the  Lepisostei  (Pholidopkoruf).  Dr.  Zittel  says  of  the  genus 
named  :  "In  der  hinteren  Caudal-region  stehendie  Hypo-und  Pteu- 
rocentren  einander  fast  gegeniiber  und  bilden  dadurch  eine  knb'cherne 
Scheide,  auf  welcher  die  untern  und  oberen  Bogen  aufsitzen." 

While  the  course  of  modification  which  has  just  been  described 
has  been  pursued  by  many,  perhaps  most,  of  the  relatives  of  Amia, 
and  possibly  by  other  fishes,  it  appears  probable  that  some,  such  as 
Cat  urns  and  Callopterus  (Zittel,  60,  pp.  221  and  230,  Figs.  241,  243) 
followed,  so  far  as  they  went,  a  different  course.  In  Caturus  the  ver- 
tebral elements  often  lack  much  of  covering  the  notochord.  Never- 
theless the  lower  intercalated  elements,  as  an  ossification  at  least,  is 
absent,  and  possibly  also  the  base  of  the  upper  arch.  Evidently  no 


42  FIELD  COLUMBIAN  MUSEUM — ZOOLOGY,  VOL.   i. 

» 

ossified  rings  have  ever  existed.  The  pleurocentrum  and  hypocen- 
trum  push  themselves  over  the  notochord  until  they  come  into  con- 
tact and  form  triangles  on  the  sides  of  the  notochord.  Whether  such 
elements  ever  continue  to  grow  around  the  notochord  and  produce 
complete  rings  I  do  not  know.  In  view  of  what  happens  in  Amia,  it 
would  appear  to  be  most  reasonable  to  deny  this  until  the  evidence  is 
made  unquestionable.  It  is  interesting  to  note  that  in  both  Caturus  and 
Callopterus,  according  to  Zittel's  account,  no  rings  appear  in  any  por- 
tion of  the  body.  Euthynotus  possibly  furnishes  us  with  a  case  in 
which  the  hypocentrum  has  grown  around  a  considerable  portion  of 
the  notochord,  while  the  pleurocentrum  is  reduced  to  small  propor- 
tions, but  the  epicentrum  is  probably  present  and  the  genus  therefore 
belongs  nearer  Eurycormus.  With  the  same  elements  to  start  with, 
the  various  genera  have  developed  a  considerable  variety  of  struc- 
ture in  their  vertebral  structure,  and  it  will  require  much  investigation 
to  discover  all  the  relationships. 

Attention  ought  to  be  called  to  the  fact  that  the  pleurocentrum 
and  the  ring  containing  it  belong  to  the  anterior  end  of  the  vertebra, 
or  the  vertebral  complex,  into  which  it  enters.  In  the  middle 
tail  region  of  Amia,  whenever,  with  rare  exceptions,  which  may  be 
regarded  as  abnormal,  the  two  vertebral  rings  unite,  the  one  contain- 
ing the  pleurocentrum  is  anterior.  In  the  dorsal  region,  it  is  the 
intercalated  cartilages  placed  in  front  of  each  arch  which  push  them- 
selves backward  beneath  the  latter  and  unites  with  the  hypocentrum 
to  form  the  centrum.  It  is  necessary  to  keep  this  in  mind  in  exam- 
ining the  text  and  figures  of  Dr.  Zittel's  Handbuch,  in  which  the 
statement  is  sometimes  made  that  the  pleurocentrum  is  the  hinder 
element. 

I  have  already,  on  page  no,  called  attention  to  Schmidt's  expla- 
nation of  the  development  of  the  dorsal  vertebrae  of  Amia.  My  invest- 
igations on  the  young  of  Amia  have  demonstrated  that  neither  of  his 
hypotheses  is  true.  There  is  no  fusion  of  two  such  simple  rings  for 
each  myomere  as  are  found  in  the  tail.  Furthermore,  the  pleurocen- 
trum is  not  suppressed  by  the  growth  of  the  hypocentrum.  Such  a 
process  as  he  describes  would  make  of  the  centrum  simply  a  hypo- 
centrum.  On  the  other  hand,  in  Amia,  the  pleurocentral  element 
forms  the  whole  upper  half  of  each  dorsal  vertebra. 

7.      FURTHER    DISCUSSION    OF    THE    VERTEBRAL    STRUCTURE    OF    THE 

TELEOSTEI. 

We  may  return  for  a  moment  to  the  consideration  of  the  verte- 
bras of  our  living  Teleosts.  Does  the  pleurocentrum  enter  into  the 


OCT.  1895.  VERTEBRAL  COLUMN  OF  AMIA — HAY  43. 

composition  of  any  of  them  ?  I  am  not  able  to  answer  definitely.  I 
am  not  aware  that  anything  like  intercalated  cartilages  has  been  found 
in  any  of  our  bony  fishes  belonging  to  the  group  of  Teleosts.  The 
Clupeidce,  as  being  most  closely  related  to  the  Ami  idee,  might  be  ex- 
pected to  throw  light  on  the  question.  In  case  that  the  cartilages 
forming  the  upper  arms  of  the  cross  found  in  the  vertebrae  of  some 
fishes,  as  Lucius  (£sox),  were  segmented  off  from  that  contained  in 
the  remainder  of  the  upper  arch,  I  should  regard  it  as  representing 
the  pleurocentrum  ;  but  I  find  mention  of  only  one  fish  showing  such 
a  condition.  This  is  the  genus  Monacanthus,  referred  to  by  Goette 
(33,  p.  129).  Usually  the  cartilage  of  the  upper  arch  comes  down  on 
the  notochord,  and  is  unbroken  from  end  to  end,  as  it  seems  to  be  in 
Lucius  and  Salmo.  It  may  be  that  in  these  the  pleurocentrum  is 
wholly  missing. 

I  do  not  think  that  there  can  be  any  question  that  the  lower  por- 
tion of  the  osseous  ring  which  encircles  the  notochord  and  forms  the 
earliest  rudiment  of  the  centrum  is  the  hypocentrum,  Does  this 
give  origin  to  all  the  bone  which  enters  into  the  centrum  ?  If  so,  the- 
opinion  of  Prof.  Cope  is  correct.  The  statements  of  Lotz,  Cartier, 
and  Goette  that  the  primitive  vertebral  ring  grows  from  the  points 
of  contact  with  the  notochord  iipward  and  meet  above  the  notochord, 
are  in  favor  of  this  idea.  If,  on  the  other  hand,  bony  centers,  how- 
ever small,  should  be  found  at  the  bases  of  the  upper  arches,  the  ver- 
tebra would  not  be  wholly  a  hypocentrum.  And  this,  I  suspect,  will 
be  found  to  be  the  case.  If  those  observations  are  correct  which  go 
to  prove  that  the  ring  starts  at  four  points,  the  fishes  in  which  this 
happens  would  have  something  more  than  hypocentra.  If  no  pleu- 
rocentra  are  developed,  the  centrum  would  be  formed  from  the  bases 
of  the  upper  and  the  lower  arches,  and  be  similar  to  those  of  the 
middle  tail  region  of  Amia  which  are  furnished  with  arches.  It  is 
extremely  probable  that  our  modern  bony  fishes  are  derived  from 
many  distinct  sources  among  the  ancient  Ganoids,  and  it  is  possible 
that  among  the  latter  were  some  which  never  developed  bony  inter- 
vertebral  elements.  And  even  among  the  relatives  of  Amia  there  were 
some,  like  Hypsocormus,  which  seem  not  to  have  the  intervertebral 
ossifications,  possibly  not  the  cartilages.  We  must  therefore  be  pre- 
pared to  find  that  the  composition  of  the  vertebral  centra  of  our  fishes 
is  various. 

The  ribs  of  Amia  deserve  a  portion  of  our  attention.  None  are 
present  in  larvae  i5mm.  long;  all  have  been  laid  down  in  cartilage 
in  specimens  23mm.  in  length.  Hence  I  cannot,  as  I  hoped  to  do, 
make  observations  on  the  method  of  their  origin,  whether  in  direct 
connection  with  the  transverse  processes  or  independent  of  them. 


44  FIELD  COLUMBIAN  MUSEUM — ZOOLOGY,  VOL.   i. 

Do  the  ribs  pass  backward  and  form  a  part  of  the  lower  arches 
-of  the  tail  ?  In  case  it  should  be  demonstrated  that  ribs  chondrify 
independently  of  the  transverse  processes,  there  are  no  ribs  in  the 
tail  of  Amia.  Otherwise  it  may  be  a  question  of  definition.  While 
there  is  a  suture  separating  the  bone  of  the  lower  arch  from  the 
vertebral  centrum  in  the  tail,  there  is  no  segmentation  of  the  carti- 
lage. The  lateral  halves  of  the  most  anterior  six  or  seven  arches 
unite  below  the  great  blood  vessels  to  form  the  haemal  canal,  and 
immediately  below  the  point  of  union  there  is  a  joint  followed  by  a 
long  spine.  This  spine  might  possibly  be  regarded  as  being  a  pair  of 
fused  ribs. 

The  ribs  and  the  transverse  processes  pass  outward  immediately 
beneath  the  peritoneum,  as  do  those  of  most,  but  not  all,  Teleostomi. 
Anteriorly  the  transverse  processes  rise  high  up  on  the  sides  of  the  noto- 
-chord ;  but,  as  already  stated,  I  have  nowhere  found  them  coalescing 
with  the  bases  of  the  upper  arches.  Scheele  has  found  the  bases  of 
the  lower  arches  in  the  most  anterior  vertebras  of  Rhodeus  to  spring 
from  a  common  mass  of  cartilage  with  the  bases  of  the  upper  arches. 
Proceeding  from  this  fact  he  concludes  that  the  Cyprinidae  are  a  more 
primitive  form  than  the  Salmonidse,  in  which  upper  and  lower  arches 
.arise  independently  of  each  other;  and  that  the  ribs  of  Teleosts  are 
homologous  with  those  of  Amphibians.  In  the  latter  conclusion  he 
wholly  ignores  the  fact,  first  demonstrated  by  Aug.  Miiller  and  later 
emphasized  by  Rabl  (50),  Hatschek,  and  Baur  (12),  that  the  ribs  of 
these  two  groups  of  animals  occupy  very  different  positions  with  ref- 
•erence  to  the  lateral  muscles,  and  the  further  fact  that  some  fishes 
possess  both  kinds  of  ribs.  As  to  the  Cyprinidae,  it  has  appeared  to 
me  that  they  are  in  many  respects  much  more  highly  differentiated 
fishes  than  the  Salmonidae.  This  is  shown  in  the  universal  absence 
of  teeth  on  the  bones  of  the  mouth,  the  great  modification  of  the 
lower  pharyngeal  bones  and  the  development  of  teeth  on  them,  the 
modification  of  the  anterior  vertebrae  to  the  service  of  hearing,  and 
the  enormous  reduction  of  the  cartilage  found  in  the  vertebral  col- 
umn of  the  lower  fishes.  Moreover,  instead  of  the  Cyprinidae  being 
more  ancient  than  the  Salmonidae,  they  appeared,  so  far  as  our  knowl- 
edge goes,  at  a  considerably  later  period,  the  beginning  of  the  Mio- 
cene ;  the  Salmonidae  near  the  beginning  of  the  Cretaceous. 

Hence,  we  have  every  reason  for  concluding  that  the  condition 
of  the  upper  and  the  lower  arches  and  the  cartilages  connected  with 
them  is  in  a  more  primitive  stage  in  the  Salmonidae  than  in  the  Cyp- 
Tinidae.  We  have  now  the  testimony  of  Amia  to  the  same  effect.  Upper 
.and  lower  arches  arise  almost  universally  independently  of  each 


OCT.  1895.  VERTEBRAL  COLUMN  OF  AMIA — HAY  45. 

other,  and  their  union  is  a  secondary  matter.  In  Rhodeus  the  coales- 
cence of  the  two  sets  of  arches  has  probably  occurred  as  a  result  of 
their  being  crowded  close  to  each  other,  the  result  of  the  lifting-  up  of 
the  lower  arches  to  give  room  for  the  contents  of  the  abdomen. 

8.       FURTHER    CONSIDERATION    OF    THE    VERTEBRAL    COLUMN     OF      LIVING 
AND    EXTINCT    AMPHIBIA. 

It  may  now  prove  profitable  to  examine  a  little  more  closely  the 
condition  of  the  vertebral  column  of  the  Amphibia,  living  and  extinct,, 
in  the  light  furnished  by  the  embryology  of  Anita. 

In  the  tail  of  Archegosaurus,  and  also  in  the  two  posterior  presa- 
cral  vertebrae  of  Chelydosaurus,  there  occur,  according  to  H.von  Meyer 
(47,  p.  104)  and  Fritsch  (Fauna  der  Gaskohle),  basal  pieces  which 
Fritsch  has  called  hypocentra  pleuralia.  These  have  already  been 
referred  to,  and  the  name  haemacentra  proposed  for  them.  We  find 
then  in  the  Stegocephali  the  same  four  vertebral  elements  that  are 
found  in  Amia  during  its  larval  condition.  Furthermore,  Fritsch  tells 
iis  that  in  the  tail  of  old  specimens  of  Arctygosaurus  there  are  indica- 
tions of  embolomerous  structure  of  the  vertebrae.  This  might  very 
naturally  be  brought  about  by  the  coossification  of  the  bases  of  the 
upper  and  lower  arches  to  form  one  centrum,  and  the  union  of  the 
pleurocentra  with  the  haemacentra  to  form  the  other.  The  identity 
of  such  a  condition  with  that  found  in  the  middle  tail  region  of  Amia 
would  be  complete.  But  should  such  double  vertebrae  not  occur  in 
Archegosaurus,  they  are  found  in  the  genera ,  Cricotus  and  Diploverte- 
bron.  Prof.  Cope  tells  us  that  such  vertebrae  are  found  throughout 
the  vertebral  column  of  Cricotus.  It  seems  to  me  that  this  arrange- 
ment must  have  arisen  here  as  it  does  in  Amia,  and  that  the  ancestors 
of  the  amphibians  possessed  both  upper  and  lower  intercalated  car- 
tilages throughout  the  length  of  the  vertebral  axis. 

On  the  composition  of  the  vertebrae  of  the  Lepospondyli,  with 
their  tubular  vertebrae,  our  studies  so  far  throw  but  little  light.  Pos- 
sibly we  may  understand  them  better  after  an  examination  of  the 
vertebral  structures  of  the  living  amphibia.  In  the  Branchisauridae 
the  thin  tubular  centra  consist,  as  already  stated,  each  of  two  lateral 
halves,  separated  dorsally  and  ventrally  by  sutures.  We  have  here 
evidence  to  the  effect  that  the  vertebral  rings  are  primitively  not 
simple. 

It  is  a  matter  of  the  highest  interest  to  explain,  if  possible,  the 
morphogeny  of  the  vertebrae  of  the  higher  fishes,  the  amphibians- 
and  the  Amniota.  Probably  in  the  case  of  none  of  these  groups  shall 
we  be  able  to  do  this  satisfactorily.  In  the  attempt  to  elucidate  the 


.46  FIELD  COLUMBIAN  MUSEUM — ZOOLOGY,  VOL.   i. 

^composition  of  the  vertebrae  of  our  living  amphibians,  I  am  aware, 
that  I  tread  on  uncertain  ground,  and  that  my  conclusions  may  be 
•  erroneous.  On  the  other  hand,  some  of  the  suggestions  may  have 
some  value. 

The  origin  and  structure  of  the  vertebrae  of  the  amphibia  have 
been  quite  as  much  discussed  as  have  the  origin  and  structure  of 
those  of  the  fishes;  and  there  has  been  the  same  lack  of  unanimity 
of  opinion.  Johannes  Muller  concluded  (49  Neur.,  p.  73)  that  in  the 
majority  of  the  members  of  the  class  the  vertebral  centrum  arises  as 
.an  ossified  integral  ring  in  the  outer  sheath  of  the  notochord.  In  the 
case  of  certain  Anura  (Pelobates,  Pseudis,  etc.),  however,  the  centra 
were  found  to  arise  wholly  from  the  upper  arches,  and  the  notochord 
took  no  part  in  the  process. 

Among  the  Urodela  Gegenbaur  (29)  recognized  the   existence 
'Of  two  sheaths  surrounding  the  notochord,  an  inner  thicker,  and  an 
outer  thinner.    XDutside  of  the  latter  is  the  skeletogenous  layer,  in 
which,  at  intervals,   are  developed  the  cartilaginous  upper   arches. 
The  bases  of  the  latter  rest  on  the  outer  sheath  of  the  notochord. 
In  the  tail,  lower  arches  possess  similar  relations.     Midway  between 
the  bases  of  the  successive  arches  there  is  formed  a  ring  of  cells,  which 
later  change  to  cartilage.    There  is  no  continuous  cartilage  surround- 
ing the  notochord.     Ossification  begins  by  the  formation  of  a  delicate 
ring  of  bone  immediately  outside  the  outer  sheath,  and  in  contact 
with  the  bases  of  the  arches.  Gegenbaur  seems  to  imply  that  the  ring 
is  complete  from  the  beginning.     Its  edges  extend  forward  and  back- 
ward until  they  approach  those  of  the  neighboring  centra.     While 
this  is  progressing,  the  cartilaginous  intervertebral  rings  have  devel- 
oped and  have  become  enclosed  each  within  the  approximating  ends 
of  two  centra.     In  some  cases  the  cartilaginous  ring  remains  short 
anterio-posteriorly ;  in  other  cases  it  grows  forward  and  backward 
so  as  to  extend  from  near  the  center  of  one  vertebra  to  that  of  the 
next  behind.     The  arches  at  an  early  stage  undergo  ossification  and 
become  continuous  with  the  corresponding  centra.     We  have  then  a 
series  of  biconcave  vertebras  alternating  with  a  series  of  cartilaginous 
rings,  which  are  enclosed  in  the  concave  ends  of  the  vertebral  centra. 
Finally,  each  cartilaginous  ring  may  become  more  or  less  segmented 
transversely,  one  portion  going  to  each  of  the  two  adjoining  centra. 
In  the  case  of  the  frogs,  Gegenbaur  regarded  the  notochord  as  being 
.surrounded  by  a  continuous  tube  of  cartilage  from  which  spring  the 
upper  arches  and  with  which  the  intervertebral  rings  are  also  con- 
nected.    Ossification  is  introduced  by  the  deposit  of  calcific  matter  in 
the  cartilage  at  the  base  of  the  upper  arches.     There  is  a  center  on 


OCT.  r&95.  VERTEBRAL  COLUMN  OF  AMIA — HAY  47 

each  side  of  the  notochord,  and  from  these  the  bone  extends  around 
it,  so  as  finally  to  form  a  ring.  From  the  ring  the  bone  spreads  up- 
ward on  the  upper  arches. 

Goette  (32)  found  in  Bombinator  a  continuous  cartilaginous  band 
along  the  upper  side  of  the  notochord,  distinct  from  the  bases  of  the 
arches.  Ossification  begins  in  this  band  by  the  appearance,  sometimes 
at  least,  of  lateral  centers  beneath  the  bases  of  the  arches.  These 
at  length  form  bony  rings.  Between  them  the  cartilages  develop 
into  intervertebral  cartilages,  which  become  cross-segmented  and 
form  the  epiphyses  of  the  vertebral  centra. 

Hasse  (36)  regards  the  vertebral  centra  of  the  Anura  as  being 
composed  principally  of  the  bases  of  the  upper  arches.  In  the  case 
of  the  Urodela,  Hasse  (35)  holds  that  the  intervertebral  cartilages  lie 
^between  the  two  sheaths  of  the  notochord;  while  the  ring  of  bone 
"which  forms  the  earliest  rudiment  of  the  centrum  arises  in  the  elas- 
tic a,  first  of  all  on  the  lower  side.  Spreading  fore  and  aft  these  ver- 
tebral centra  come  to  enclose  the  intervertebral  cartilages  in  their 
concave  ends.  Later,  the  cartilages  divide,  and  a  portion  of  each  is 
distributed  to  each  of  the  two  enclosing  vertebrae. 

On  the  side  of  the  palaeontologists,  von  Meyer  (47,  p.  95,  seq.)y 
accepting  the  view  that  the  vertebral  centrum  originates  as  a  ring 
independently  of  the  arches,  concludes  that  in  such  forms  as  Archego- 
saurus  the  vertebral  column  is  in  an  embryonic  condition,  and  that 
there  are  no  centra  present. 

As  already  stated,  Prof.  Cope  regards  the  vertebrae  of  the  mod- 
ern amphibians,  like  that  of  the  Teleostomi,  as  being  derived  wholly 
from  the  hypocentra. 

On  page  123  of  this  paper  I  have  called  attention  to  the  inter- 
vertebral rings  of  cartilage  which,  in  a  certain  stage  of  development, 
surround  the  notochord  of  Lepisosteus.  and  I  have  there  suggested 
that  these  rings  occupy  exactly  the  positions  occupied  by  the  interca- 
lated cartilages  of  related  fishes.  The  fusion  of  these  cartilages 
with  one  another  to  form  a  ring,  and  their  further  fusion  with  the 
bases  of  the  neighboring  arches,  is  a  process  which  might  take  place 
secondarily.  If  this  supposition  is  allowable  in  the  case  of  Lepisosteus, 
less  objection  can  be  urged  in  the  case  of  the  Urodeles;  since 
here  the  cartilages  in  question  at  no  time  coalesce  with  the  bases  of 
the  arches.  We  might  easily  explain  the  case  by  supposing  that  the 
four  intercalated  cartilages  belonging  to  each  segment  have  fused 
and  formed  a  ring ;  that  this  has  remained,  at  least  for  a  long  time, 
in  a  state  of  cartilage ;  and  that  the  vertebral  bands  of  bone  in  front 
..and  behind  it  have  expanded  over  it  and  enclosed  it  between  them. 


48  FIELD  COLUMBIAN  MUSEUM — ZOOLOGY,   VOL.   i. 

One  objection  against  this  hypothesis  may  be  urged  in  the  case 
of  Lepisosteus  and  all  the  amphibians.  In  all  of  these  the  interver- 
tebral  ring  becomes  cross-segmented,  and  the  parts  are  distributed 
to  different  vertebrae,  the  anterior  portion  becoming  the  hinder  end 
of  the  vertebra  in  front,  the  hinder  portion  the  front  end  of  the  ver- 
tebra behind  it.  In  answer  to  this  objection  it  may  be  said  that  orig- 
inally the  intervertebral  ring,  whatever  its  origin,  is  an  integral  mass 
of  cartilage  ;  that  is,  after  the  fusion  of  the  circle  of  constituent 
pieces  ;  and  that  the  transverse  segmentation  is  also  a  secondary 
matter.  It  certainly  would  not  be  difficult  to  find  examples  of  this 
secondary  segmentation  of  cartilage  in  many  animals. 

A  further  objection  against  homologizing  the  invertebral  carti- 
lages of  the  Urodeles  with  the  intercalated  cartilages  of  Amia,  may 
be  found  in  the  apparent  fact  that  the  intervertebral  ring  of  the  Uro- 
deles is  located  between  the  inner  and  the  outer  sheaths  of  the  noto- 
chord.  Hasse's  observations  (35)  appear  to  prove  that  such  is  the 
fact ;  nevertheless,  it  is  desirable  that  they  shall  be  confirmed.  Geg- 
enbaur  did  not  reach  the  same  conclusion.  Hasse,  in  the  paper  just 
referred  to,  and  elsewhere,  regards  the  intercuticular  position  of  the 
cartilages  as  indicating  a  relationship  between  the  Elasmobranchs 
and  the  Dipnoi,  on  the  one  hand,  and  the  Urodeles  on  the  other. 
Later  (39,  p.  91)  he  concludes  that,  as  regards  the  Dipnoi,  he  is  prob- 
ably wrong,  and  that  the  just  named  group  does  not  stand  in  close 
relation  with  the  Urodeles.  The  so-called  elastica  externa  of  Dipnoi 
and  the  cartilaginous  Ganoids  may,  after  all,  be  the  homologue  of  the 
inner  sheath  of  Elasmobranchs. 

In  view  of  these  difficulties  and  doubts  it  appears  to  be  easier  to 
believe  that  the  intercalated  cartilages  have,  through  pressure  or  some 
other  influence,  caused  the  elastica  to  be  dissolved,  and  have  thus 
come  to  lie  in  contact  with  the  inner  sheath.  It  is  to  be  noted  that 
the  groups  of  cells  which,  in  the  salamanders,  give  origin  to  the  inter- 
vertebral rings,  are  placed  exactly  where  we  should  expect  the  inter- 
calated cartilages  to  appear.  In  T-jito:*  tceniatus,  investigated  by 
Hasse,  these  appear  in  the  intervals  between  the  successive  arches 
above  ;  while  on  the  lower  side  of  the  notochord,  they  form  one  cen- 
ter in  the  middle  line,  as  though  from  a  coalescence  of  the  two  lateral 
masses. 

Gegenbaur  attached  much  importance  to  the  existence  of  the 
intervertebral  cartilages  in  the  vertebral  column  of  the  amphibians. 
He  says,  "Allen  aber  ist  mit  Auftreten  des  Intervertebralknorpels 
ein  eigenthiimliches  Unterscheidungsmoment  gegen  die  Fische 
hingeworden.  und  in  dieser  neuen  Bildung  is  zugleich  eine  fur  die 


OCT.  1895.  VERTEBRAL  COLUMN  OF  AMIA — HAY  49 

ganze  kiinftige  Gestaltung  des  Wirbelkorpers  maasgebende  Einrich- 
tung  zu  Stande  gekommen."  It  is  not  impossible,  however,  that  we 
have  here,  after  all,  no  new  structures,  but,  as  in  so  many  other 
cases,  only  new  adaptations  and  new  combinations  of  structures 
already  well  known  in  lower  forms, 

To  what  extent  the  bases  of  the  lower  arches,  the  hypocentra, 
may  be  represented  in  the  trunk  region  of  the  Urodeles  is  questiona- 
ble. Possibly  with  the  disappearance  of  the  lower  series  of  ribs  the 
bases  of  the  arches  also  have  totally  disappeared.  This  seems  to  be 
the  condition  of  the  Anura,  certainly  in  the  case  of  those  with  epi- 
chordal  vertebrae.  But  evidences  of  hypocentral  ossifications  should 
be  looked  for  in  the  Urodeles  in  the  trunk,  and  such  ossifications  are 
certainly  present  in  the  tail. 

The  opinion  of  Prof.  Cope  that  the  vertebral  centra  of  the  Am- 
phibians are  represented  by  only  the  hypocentra  was  doubtless  the 
outcome  of  the  idea  that  only  pleurocentra  and  hypocentra  enter  into 
the  composition  of  centra.  That  the  bases  of  the  upper  arches  and 
haemacentral  bones  may  also  participate  in  the  composition,  there  can 
now  be  no  doubt. 

In  the  "  Biologisches  Centrallblatt,"  Band  vi.,  1888,  Dr.  G.  Baur 
has  discussed  the  morphogeny  of  the  vertebral  column  and  given  the 
history  of  the  question  and  the  literature  bearing  on  the  subject.  The 
view  proposed  first  by  Cope,  and  accepted  by  Albrecht,  Dollo  and 
Baur,  that  the  vertebral  centrum  of  Amniota  has  been  derived  from 
the  pleurocentrum  is,  I  believe,  correct.  The  evidences  in  favor  of 
this  hypothesis  have  been  presented  by  Baur  in  the  paper  just  cited. 
A  consideration  of  the  situations  in  which  the  various  elements  con- 
nected with  and  forming  the  vertebra  confirms  the  hypothesis. 

The  arches,  upper  and  lower,  of  the  Amniota  are  unquestion- 
ably homologous  with  those  of  the  lower  vertebrates,  and,  as  in  the 
latter,  are  developed  in  the  intersection  of  two  sets  of  membranous 
septa,  viz. :  those  between  the  myomeres  and  those  between  the  two 
sides  of  the  body,  including  in  the  latter  the  subperitoneal  membrane. 
The  hypocentra,  therefore,  are  cut  by  the  transverse  septa.  The 
intercalated  cartilages,  or  pleurocentra,  on  the  other  hand,  fall  be- 
tween the  septa  and  in  the  myorneres.  When  the  hypocentrum  enters 
into  the  composition  of  the  vertebral  centrum,  the  lower  arches  will 
naturally  be  found  intimately  connected  with  the  centrum.  And  such 
is  its  position  in  all  the  living  tailed  amphibians  (Stannius,  Am- 
phibia, page  n)  being  attached  to  the  middle  or  hinder  half  of  the 
centrum.  In  the  fossil  Hylonomus  fritschi,  Credner,  however,  the 
lower  arches  are  represented  as  being  attached  between  two  contig. 


50  FIELD  COLUMBIAN  MUSEUM — ZOOLOGY,  VOL.   i. 

uous  vertebrae.     This  condition  I  am  not  at  present  able  to  explain. 

If  now  the  hypocentrum  should  vanish  and  its  place  be  taken  by 
the  enlarged  pleurocentrum,  as  is  believed  to  be  the  case  among 
the  Amniota,  the  bases  of  the  lower  arches,  if  present,  would 
primarily  fall  between  the  vertebral  centra.  And  it  is  between 
the  vertebrae,  or  close  to  their  articulation,  that  we  find  the  attach- 
ments of  the  lower  arches,  or  chevron-bones,  of  most  of  the  higher 
vertebrates.  The  departures  from  the  rule  may  be  easily  explained 
as  secondary  modifications. 

The  upper  arches,  like  the  lower,  are  developed  in  the  transverse 
septa.  This  being  the  case,  the  connection  of  the  arches  with  the 
pleurocentra  must  be  secondary.  Hasse,  in  his  "  Beitrage  zur  Allge- 
meinen  Stammesgeschichte  der  Wirbelthiere,"  appears  to  have  op- 
posed this  view,  regarding,  as  other  writers  have  done,  the  arches  as 
developing  in  direct  union  with  the  centra.  On  the  other  hand,  Fro- 
riep  (27)  holds  that  the  body  of  the  vertebra  has  an  origin  independ- 
ent of  the  arches.  The  arch  is  the  fundamental  and  earliest  struc- 
ture, the  centrum  a  secondary  one.  He  rejects  the  hypothesis  that 
the  vertebral  body  of  the  higher  vertebrates  proceeds  from  the  union 
of  the  basal  portions  of  the  arches.  According  to  Froriep,  the  prim- 
itive membranous  arches  grow  around  the  notochord  and  unite  below 
the  latter  to  form  his  "  hypochordale  Spange."  The  latter  is  evi- 
dently the  representative  of  the  hypocentrum.  The  upper  arch  at 
length  chondrifies  and  unites  with  the  centrum  next  behind.  The 
latter  is  the  pleurocentrum.  The  shifting  of  the  arch  backward  to 
become  attached  to  the  pleurocentrum  reminds  us  of  the  movement 
of  the  arches  of  Amia  to  join  partly  the  pleurocentrum  next  behind. 
Hoffman  (40)  tells  us  that  in  the  tortoises  the  ribs  and  the  upper 
arches,  during  the  early  stages  of  development,  rest  intervertebrally 
on  the  cartilaginous  tube  which  surrounds  the  notochord.  According 
to  Gegenbaur,  there  is,  in  Lacertilia,  a  stage  in  which  the  upper  arch 
is  placed  intervertebrally.  (29,  p.  44).  The  ribs  of  the  amphibia 
being  developed  in  the  transverse  septa,  must  have  their  connection 
primitively  with  the  hypocentra,  rather  than  with  the  pleurocentra. 
It  has  been  shown  by  Cope  (14,  p.  518)  that  in  some  of  the  Pelyco- 
sauria  (Theriodontia)  the  head  of  the  rib  is  attached  to  the  intercen- 
trum ;  and  Dr.  Baur  has  pointed  out  (6,  8)  that  this  is  true  also  in  the 
case  of  the  cervical  vertebrae  of  the  very  primitive  reptile  Spheno- 
don,  of  those  of  the  Crocodilia,  and  of  those  of  some  of  the  Dino- 
sauria.  When  now  the  hypocentrum  becomes  rudimentary  or  disap- 
pears, the  head  of  the  rib  will,  at  first  at  least,  be  attached  between 
the  pleurocentra,  now  become  the  centra.  Such  is  its  attachment  in 


OCT.  1895.  VERTEBRAL  COLUMN  OF  AMIA — HAY  51 

a  large  number  of  the  Amniota.  As  a  result  of  subsequent  modifi- 
cations, the  rib-head  may,  of  course,  form  an  attachment  with  the 
centrum,  usually  with  the  one  next  behind ;  occasionally  to  the  hinder 
end  of  the  one  in  front. 

In  case  the  rib  develops  a  second  point  of  attachment  to  the  ver- 
tebral elements,  this  will  naturally  be  with  the  upper  arch,  since  rib 
and  arch  lie  in  the  same  transverse  septum ;  the  tubercular  portion  of 
the  rib  will  also  be  carried  backward,  and  this  may  have  some  in- 
fluence in  causing  also  the  head  of  the  rib  to  take  a  more  posterior 
articulation.  As  a  matter  of  fact,  the  tubercular  process  of  the  ver- 
tebra usually  springs  from  the  upper  arch.  The  Ichthyosauria  fur- 
nish us  with  a  case  in  which  the  tubercular  attachment  has  descended 
low  down  on  the  centrum.  In  the  dorsal  region  of  the  Crocodilia  the 
rib-heads  also  desert  the  centra  and  adhere  to  the  transverse  pro- 
cesses. 

We  have  seen  that  in  Amia  the  pleurocentrum,  both  in  the  dor- 
sal and  in  the  middle  portion  of  the  tail,  goes  to  form  the  anterior 
portion  of  the  vertebra  to  which  it  belongs.  On  the  contrary,  Fro- 
riep  holds  that  the  upper  arch,  rib,  and  "hypochordale  Spange"  belong 
primarily  to  the  centrum  immediately  behind  them,  thus  making  the 
hypocentrum  anterior.  The  true  explanation  may  be  that  the  hypo- 
centrum  and  the  elements  connected  with  it  belong  no  more  to  the 
pleurocentrum  behind  it  than  to  the  one  in  front.  It  is  then  free  to 
form  connection  with  either,  and  this  connection  is  different  in  the 
different  groups  of  vertebrates. 

In  concluding  this  paper  I  wish  to  acknowledge  my  indebtedness 
to  Dr.  George  Baur  for  the  opportunity  to  conduct  my  investigations 
in  his  laboratory  in  the  University  of  Chicago,  and  for  many  val- 
uable suggestions  offered  during  the  progress  of  my  work. 


52  FIELD  COLUMBIAN  MUSEUM — ZOOLOGY,  VOL.  i. 

<« 

BIBLIOGRAPHY. 

1.  Allis,  Edw.  P.,    1888.    The  Anatomy  and  Development  of  the  Lateral  Line 
System    in    Amia  calva.      Journal    of    Morphology,    Vol.    II.     pp.    463 — 566.      Pis., 
XXX-XLII. 

2.  Baer,  Ernest  v.      1835.     Untersuchungen    iiber    die  Entwicklungsgeschichte 
der  Fische. 

3.  Balfour,   P.M.     1881.     A  Treatise  on  Comparative  Embryology.     Vol.  II. 

4.  Balfour,  F  M   and  Parker,  W.  K.  1883.    The  Structure  and  Development  of 
Lepidosteus.     Transactions  of    the  Philosophical   Society;    also  in  Memorial  edition 
of  works  of  F.  M.  Balfour.  1885,  Vol.  I,  pp   738-  847.    Pis.  34—42. 

5.  Baur,  G.     1886.     Ueber   die   Morphogenie   der   Wirbelsaule   der  Amnioten. 
Biologisches  Centralblatt,  Band  VI.  S.  332—342.  353—303. 

6. 1886.  The  Ribs  of  Sphenodon  (Hatteria).  American  Naturalist,  Vol.  XX., 

pp.  979—981. 

7. 1886.  Proatlas,  Atlas,  and  Axis  of  the  Crocodilia.  Amer.  Nat.,  Vol.  XX., 

pp.  288—293. 

8. Osteologische  Notizen  iiber  Reptilien.  Zoologischer  Anzeiger,  Bd.  IX.,  S. 

733—743. 

10. 1887.    On  the  Morphology  of  Ribs.    Amer.  Nat.,  Vol.    XXI.,  pp.  942-945. 

11. 1887.  Arrangement  of  the  Sauropsida.  Journal  of  Morphology,  Vol.  I.,  pp. 

93—104. 

12. 1893.  Ueber  Rippen  und  ahnliche  Gebilde  und  deren  Nomenclatur.  Anat- 

omischer  Anzeiger,  Jahrgang  IX,,  S,  116 — 120. 

13.  Cartier,  O.  1875.  Beitrage  zur  Entwicklungsgeschichte  der  Wirbelsaule. 
Zeitschrift  fur  wissenschaftliche  Zoologie,  Bd.  XXV..  Sup.,  S.  65-70. 

14  Cope,  Edward  D.  1878.  Descriptions  of  Extinct  Batrachia  and  Reptilia 
from  the  Permian  Formation  of  Texas.  Palaeontological  Bulletin  No.  29,  pp.  505- 
530  (Extracted  from  the  Proceedings  of  the  Amer.  Phil.  Soc.,  1878.) 

15. 1880.  Second  Contribution  to  the  History  of  the  Vertebrata  of  the  Permian 

Formation  of  Texas.  Palaeontological  Bulletin  No.  32,  pp.  1 — 22.  (From  Proc.  Amer. 
Phil.  Soc.,  1880.) 

16. 1882.  The  Rhachitomous  Stegocephali.  Amer.  Nat.,  Vol.  XVI.,  pp. 

334—335. 

17. 1883.  The  Vertebrata  of  the  Tertiary  Formations  of  the  West.  Washing- 
ton, D.  C. 

18. 1884.  The  Batrachia  of  the  Permian  Period  of  North  America.  American 

Nat,  Vol.  XVII  ,  pp.  26—39. 

19, 1886.    The  Batrachian  Intercentrum.  Amer.  Nat.,  Vol.  XX.,  pp.  76  ;  175. 

20. 1886.  On  the  Intercentrum  of  the  Terrestrial  Vertebrata.  Trans,  Amer. 

Phil  Soo.,  Vol.  XVI.,  pp.  243—253. 

21. 1887.  The  Homology  of  the  Chevron  Bones.  Amer.  Nat.,  Vol.  XII., 

p.  319. 

22. Zittel's  Manual  of  Palaeontology.    Amer.  Nat.,  Vol.  XXI,,  pp.  1014—1019. 

23.  Credner,  Hermann.     1881—1886.     Die  Stegocephalen  und  Saurier  aus  dem 
Rothliegenden   des    Plauen'schen   Grundes   bei  Dresden.     Zeitschrift  der  deutschen 
geologischen  Gesellschaft,   Bd.    XXXIII.,  1881;   XLV.,  1893;  Naturwissenschaftliche 
Wochenschrift,   Bd.  V.,  Berlin,  1890. 

24.  Deecke,  W.    Ueber  Fische  aus  verschiedenen  Horizonten  der  Trias.   Palaeon- 
tographica,  Bd.  XXXV.,  pp.  97—138.  Taf.  VI,  VII. 


VERTEBRAL  COLUMN  OF  AIMIA — HAY.  53 

25.  Dumeril,     Aug.    1870.     Histoire  naturelle   des   Poissons    ou     Ichthyologie 
Generalle.     Tome  II. 

26.  Franque,  Henricus,     1847.     Nonnulla  ad  Amiam  calvam  accuratius  cognos- 
cendam.     With  one  plate. 

27.  Froriep,    Aug.     1886.    Zur  Entwicklungsgeschichte    der    Wirbelsaule.     II. 

/Beobachtung  an  Saugethieren. 
28.     Gegenbaur,  C.     1867.     Ueber   die  Entwicklung  der  Wirbelsaule  des  Lepid- 
osteus  mit   vergleichenden  anatomischen  Bemerkungen.     Jenaische  Zeitschrift,  Bd. 
III. 

29. 1862.     Untersuchungen  zur  vergleichenden  Anatomie  der  Wirbelsaule  bei 

Amphibien  und  Reptilien.     Vier  Tafeln. 

30. 1876.      Einige   Bemerkungen  zu   Goette's    "Entwicklungsgeschichte   der 

Unke."     Morphologisches  Jahrbuch,   I.,  288 — 345. 

31.  Gill,  Theodore.     1871.     Arrangement  of  the  Families  of  Fishes.     Washing- 
ton, D.  C. 

32,  Goette,  Alex.     1875.     Die  Entwicklungsgeschichte  der    Unke.     With  Atlas 
of  22  plates, 

33. 1879.      Beitrage   zur  Morphologic   des   Skeletsystems   der  Wirbelthiere. 

Archiv  fur  mikroskopische  Anatomie,  Bd.  XVI,  117—152;  Taf.  VII— IX. 

34.     Grassi,  B.     1883.     Developpement  de  la  Colonne  vertebrale  chez  les  Pois- 
sons osseux.     Archives  Itallienne  de  Biologic.     Tome  IV.,  pp.  236—244;  251 — 268. 
J          35.     Hasse,  C.     1890.     Die  Entwicklung  der  Wirbelsaule  von    Triton  t<enialus. 
Zeitschrift  fur  wissenschaftliche  Zoologie,  Bd.  LIII.,  Sup.  S.,  1-20.   Taf.   I. -III. 

36. 1892.     Die  Entwicklung  der  Wirbelsaule  der  ungeschwanzten  Amphibien. 

Zweiter  Abhandl.    Mit  Tafel  XII.    Zeitschr.  f.  wiss.  Zoologie.  Bd.  LV.,  S.  252-264. 

37. 1892.     Die  Entwicklung  der  Wirbelsaule  der  Elasmobranchier.     Dritter 

Abhandl.     Mit  Tafel  XXL.     Zeitschr.  f.  wiss.   Zoologie,  Bd,  .LV.,    S.    519-531. 

38. 1892.    Die  Entwicklung  der  Wirbelsaule  der  Dipnoi.    Vierte  Abhandl.  Mit 

Tafel  XXII.     Zeitschr.  f.  wiss.  Zoologie,  Bd.  LV.,  S.  533-542. 

39. 1893.     Die  Entwicklung   und  der   Bau  der   Wirbelsaule  der   Ganoiden. 

Fiinfte  Abhandl.  Mit  Tafeln   V— VII.      Zeitschr.    f.    wiss.  Zoologie,   Bd.    LVII.  S. 
76— !>(i. 

40.  Hoffman,  C.  K.  1878.     Beitrage  zur  vergleichenden  Anatomie  der  Wirbel- 
theire.  VIII.  Ueber  die  Chorda  dorsalis  bei  den  Schildkroten.   Niederlandisches  Archiv 
fur  Zoologie,  Bd.  IV,  pp.  185-199;  Taf.  XII. 

41.  Klaatsch,  H.     1893.       Beitrage   zur  vergleichenden  Anatomie  der  Wirbel- 
saule.    I.  Ueber  den  Urzustand  der  Fischwirbelsaule,  (Mit  Taf.   XXVI.  und  eine  Fig- 
urimText.)      Morphologisches  Jahrbuch,  Bd.  XIX.,  pp.  649—680. 

42. 1893.    Beitrage  zur  vergleichenden  Anatomie  der  Wirbelsaule.    II.  Ueber 

die  Bildung  knorpeliger  Wirbelkorper  bei  Fischen.     (Mit  Taf.  VII,  und  6  Figuren  im 
Text.)     Morphologisches  Jahrbuch,  Bd.  XX.,  S.  143—186. 

43.  Kolliker,  Albert.     1860.     Ueber   das   Ende  der  Wirbelsaule  der  Ganoiden 
und  einige  Teliostier.     Mit  4  Tafeln. 

44.  Leidy,  Joseph.     1873.     Contributions  to   the   Extinct  Vertebrate  Fauna  of 
the  Western  Territories.     Report  U.  S.  Geological  Survey  of  the  Territories,  Vol.  I., 
Pt.  I.,  pp.  358,  Pis.  I-XXXVII.     Washington,  D.  C. 

45.  Lotz,  Theophil.     1864.     Ueber  den  Bau   der  Schwanzwirbelsaule  der  Sal- 
moniden,  etc.    Zeitschrift  fur  wissenschaftliche  Zoologie,  Bd.  XIV.,  pp.  81 — 106;  Taf. 
X.-XIII. 


54  FIELD  COLUMBIAN   MUSEUM — ZOOLOGY,  VOL.  i. 

46.  Liitken,  Chr.   von.      1873.      Ueber   die  Begrenzung   und   Eintheilung  der 
Ganoiden.     Palaeontographica,  Bd.  XXII.,  S,    1-54. 

47.  Meyer,  Hermann  von.     1857.     Reptilien   ausder  Steinkohlen-Formation  in 
Deutschland.  Zweite  Lieferung.    Palaeontographica,  Bd.  VI.    S.    59-218;  Taf.   VIII— 
XXIII. 

48.  Miiller,  August.     1853.     Beobachtungen   zur  vergleichenden  Anatomic  der- 
Wirbelsaule.     Archiv  fiir  Anatomic  und  Physiologic. 

49.  Miiller,  Johann.     1835 — 1845.     Vergleichende  Anatomie  der  Myxinoiden. 

50.  Rabl,  Carl.     1893.     Theorie  des  Mesoderms,  II.    (Mil  Taf.  IV— VII. ;   Fig. 
10-13  imText.)     Morphologisches  Jahrbuch,  Bd,  XIX.,  S.  G5— 144. 

51.  Rathke,  Heinrich.     1839.     Entwicklungsgeschichte  der  Natter. 

52.  1866.     Untersuchungen  iiber  dieEntwicklung  und  den  Korperbau  der  Krok- 
odilen. 

53.  Reis,  Otto  M.   1888.    Die  Coelacanthinen,   mit  besonderer  Beriicksichtgung 
der  im  weissen  Jura  Bayern  vorkommenden   Arten.     Palaeontographica,   Bd,  XXV., 
S.  1—96.,   Taf.  I— V. 

54.  Sagemehl,  M.     1883.     Beitrage  zur  vergleichenden  Anatomie  der  Fische. 
I.   Das  Cranium  von  Amia  calva.     Morphologisches  Jahrbuch,  Bd.  IX.,  S.  177. 

55.  Scheele,  C.     1893.     Beitrage   zur   Entwicklungsgeschichte   der   Teliostier- 
Wirbelsaule.     Morphologisches  Jahrbuch,  Bd.  XX.,  S.    1—47,  Taf  I.— III. 

56.  Schmidt,  Ludwig,     1892.     Untersuchungen  zur  Kenntniss  des  Wirbelbaues 
von  Amia  calva.     Zeitschrift  fiir  wissenschaftliche  Zoologie,  Bd.  LIV.,  S   748 — 764' 
Taf.  XXXIV. 

57.  Shufeldt,  R.  W.     1885.     The  Osteology  of  Amia  calva,  etc.     From  Report 
of  U.  S.  Commission  of  Fish  aud  Fisheries  for  1883.     PI.  I. — XIV.    Contains  transla 
tion  of  Sagemehl's  paper. 

58.  Stannius,  Hermann.     1854.     Handbuch  der  Anatomie  der  Wirbelthiere. 

59.  Wilder,  B.  G.     1877.     On  the  Tail  of  Amia.      Proceedings  of  the  Ameri- 
can Association  for  the  Advancement  of  Science  for  1876.     Pp.  264 — 266. 

60.  Zittel,  Carl   von.     1887—1890.     Handbuch  der  Palaeontologie.      Bd.    Ill; 
Pisces,  Amphibia,  Reptilia,  und  Aves. 


PLATES. 

EXPLANATION  OF  FIGURES, 
ao.     Aorta, 
as.     Aortal  support, 
cu.  ch.     Inner  notochordal  sheath. 
e.  ex.     External  elastica. 
h.  a.     Haemal  arch. 

i.  c.     Cartilage  intercalated  between  halves  of  upper  arch  above  the  spinal  cord. 
1.  1.  s.     Superior  longitudinal  ligament, 
n.     Nerve. 

n.  a.     Half  of  neural  arch, 
not.     Notochord. 

n,  s.     Distal  extremity  of  lateral  half  of  neural  arch, 
par.     Parapophysis. 

p.   c      Cartilage  supporting  lateral  half  of  neural  arch  (pleurocentrum.) 
r.     Rib. 

s.  n.     Spinal  nerve, 
sp.  c.     Spinal  cord, 
sp.  s.     Spinal  ganglion, 
v.     Vein. 
In  the  colored  figures  cartilage  is  represented  by  blue,  bone  by  red. 


.V! 

\  lo  sbiz  i\al  adt  io  noilsBlqoq^ri  bns  noitefilqo^rf  adJ  zin9?.3iq?>i  atfilq  eidT 
-o)odq  moiT      .snod  Isdoun  adJ  }o  n-?vi§  oats  ai  wsiv  A      v/ofad  moi^  nf»?  • 


PLATE  IV. 

This  plate  represents  the  hyoplastron  and  hypoplastron  of  the  left  side  of  Proto- 
stega  gigas  seen  from  below  A  visw  is  also  given  of  the  nuchal  bone.  From  photo- 
graph. 


FIELD  COLUMBIAN  MUSEUM. 


ZOOLOGY,  PL.  IV 


PROTOSTEGA  GIGAS. 


.V 


sno'uisnq 
}o  bns 


aril  wodf?  ol 
Blqtqa  adJ  lo 


ad} 


io  noitsBlq  aril  lo  noil£io)a9i   Ir.h'icq  A 
.allanKJnol  adl  ioasis  aril  bn«  xanod  aril  Jo 
la  SIB  Bilafllqidqix  adt 


PLATE  V. 

A  partial  restoration  of  the  plastron  of  Protostega,  to  show  the  relative  positions 
of  the  bones  and  the  size  of  the  fontanelle.  Only  the  bases  of  the  epiplastra  and  of 
the  xiphiplastra  are  shown. 


FIELD  COLUMBIAN  MUSEUM. 


ZOOLOGY,  PL.  V. 


PROTOSTEGA  GIGAS. 


-' 


H 


W   ''.A>^V 


r 


